Ensure that MBEDTLS_USE_PSA_CRYPTO is only defined when it should be

MBEDTLS_USE_PSA_CRYPTO should only be defined in Mbed OS when the
appropriate Mbed OS flags are set.

features/mbedtls/importer/adjust-config.sh

@@ -123,6 +123,10 @@ conf unset MBEDTLS_PLATFORM_TIME_TYPE_MACRO
 # which should fit RSA 4096 bit keys.
 conf set MBEDTLS_MPI_MAX_SIZE     512
 
+# Explicitly unset MBEDTLS_USE_PSA_CRYPTO as this will be set based on the
+# FEATURE_PSA flag in Mbed OS
+conf unset MBEDTLS_USE_PSA_CRYPTO
+
 # add an #ifndef to include config-no-entropy.h when the target does not have
 # an entropy source we can use.
 append_code                                                                                       \