Update copyright notices to use Linux Foundation guidance

As a result, the copyright of contributors other than Arm is now
acknowledged, and the years of publishing are no longer tracked in the
source files.

Also remove the now-redundant lines declaring that the files are part of
MbedTLS.

This commit was generated using the following script:

# ========================
#!/bin/sh

# Find files
find '(' -path './.git' -o -path './3rdparty' ')' -prune -o -type f -print | xargs sed -bi '

# Replace copyright attribution line
s/Copyright.*Arm.*/Copyright The Mbed TLS Contributors/I

# Remove redundant declaration and the preceding line
$!N
/This file is part of Mbed TLS/Id
P
D
'
# ========================

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/tests/include/test/helpers.h b/tests/include/test/helpers.h
index 69d882c..c4979cc 100644
--- a/tests/include/test/helpers.h
+++ b/tests/include/test/helpers.h
@@ -6,7 +6,7 @@
  */
 
 /*
- *  Copyright (C) 2020, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -20,8 +20,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #ifndef TEST_HELPERS_H
diff --git a/tests/include/test/macros.h b/tests/include/test/macros.h
index aaf13ad..7177156 100644
--- a/tests/include/test/macros.h
+++ b/tests/include/test/macros.h
@@ -5,7 +5,7 @@
  */
 
 /*
- *  Copyright (C) 2020, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -19,8 +19,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #ifndef TEST_MACROS_H
diff --git a/tests/include/test/psa_crypto_helpers.h b/tests/include/test/psa_crypto_helpers.h
index 8cd361f..c8013a1 100644
--- a/tests/include/test/psa_crypto_helpers.h
+++ b/tests/include/test/psa_crypto_helpers.h
@@ -2,7 +2,7 @@
  * Helper functions for tests that use the PSA Crypto API.
  */
 /*
- *  Copyright (C) 2019, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -16,8 +16,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #ifndef PSA_CRYPTO_HELPERS_H
diff --git a/tests/include/test/psa_helpers.h b/tests/include/test/psa_helpers.h
index 352ae67..f438a71 100644
--- a/tests/include/test/psa_helpers.h
+++ b/tests/include/test/psa_helpers.h
@@ -2,7 +2,7 @@
  * Helper functions for tests that use any PSA API.
  */
 /*
- *  Copyright (C) 2019, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -16,8 +16,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #ifndef PSA_HELPERS_H
diff --git a/tests/include/test/random.h b/tests/include/test/random.h
index e085f16..5e7e4e6 100644
--- a/tests/include/test/random.h
+++ b/tests/include/test/random.h
@@ -6,7 +6,7 @@
  */
 
 /*
- *  Copyright (C) 2020, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -20,8 +20,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 #ifndef TEST_RANDOM_H