Remove mbedtls_ prefix from bignum test cases

Align 2.28 with development to make backports easier.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/generate_bignum_tests.py b/tests/scripts/generate_bignum_tests.py
index c76294c..fd677ae 100755
--- a/tests/scripts/generate_bignum_tests.py
+++ b/tests/scripts/generate_bignum_tests.py
@@ -196,7 +196,7 @@
 class BignumCmp(BignumOperation):
     """Test cases for bignum value comparison."""
     count = 0
-    test_function = "mbedtls_mpi_cmp_mpi"
+    test_function = "mpi_cmp_mpi"
     test_name = "MPI compare"
     input_cases = [
         ("-2", "-3"),
@@ -217,7 +217,7 @@
 class BignumCmpAbs(BignumCmp):
     """Test cases for absolute bignum value comparison."""
     count = 0
-    test_function = "mbedtls_mpi_cmp_abs"
+    test_function = "mpi_cmp_abs"
     test_name = "MPI compare (abs)"
 
     def __init__(self, val_a, val_b) -> None:
@@ -228,7 +228,7 @@
     """Test cases for bignum value addition."""
     count = 0
     symbol = "+"
-    test_function = "mbedtls_mpi_add_mpi"
+    test_function = "mpi_add_mpi"
     test_name = "MPI add"
     input_cases = combination_pairs(
         [