Disable MBEDTLS_MEMORY_BUFFER_ALLOC_C after config.pl full

Enabling memory_buffer_alloc is slow and makes ASan ineffective. We
have a patch pending to remove it from the full config. In the
meantime, disable it explicitly.
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 32ec5fa..75a51e0 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -877,6 +877,7 @@
 component_test_se_full () {
     msg "build: full config + MBEDTLS_PSA_CRYPTO_SE_C"
     scripts/config.pl full
+    scripts/config.pl unset MBEDTLS_MEMORY_BUFFER_ALLOC_C
     scripts/config.pl set MBEDTLS_PSA_CRYPTO_SE_C
     make CC=gcc CFLAGS='-Werror -Wall -Wextra -O2 -fsanitize=address' LDFLAGS='-fsanitize=address'