Make mypy unconditional

Running mypy was optional for a transition period when it wasn't installed
on the CI. Now that it is, make it mandatory, to avoid silently skipping an
expected check if mypy doesn't work for some reason.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/check-python-files.sh b/tests/scripts/check-python-files.sh
index 449803a5..dbf0365 100755
--- a/tests/scripts/check-python-files.sh
+++ b/tests/scripts/check-python-files.sh
@@ -17,7 +17,7 @@
 
 # Purpose: check Python files for potential programming errors or maintenance
 # hurdles. Run pylint to detect some potential mistakes and enforce PEP8
-# coding standards. If available, run mypy to perform static type checking.
+# coding standards. Run mypy to perform static type checking.
 
 # We'll keep going on errors and report the status at the end.
 ret=0
@@ -72,12 +72,9 @@
     ret=1
 }
 
-# Check types if mypy is available
-if can_mypy; then
-    echo
-    echo 'Running mypy ...'
-    $PYTHON -m mypy scripts/*.py tests/scripts/*.py ||
-      ret=1
-fi
+echo
+echo 'Running mypy ...'
+$PYTHON -m mypy scripts/*.py tests/scripts/*.py ||
+  ret=1
 
 exit $ret