Remove redundant empty slot count check

USE_PSA_DONE() already checks that there are no used key slots.

The call to TEST_ASSERT() wouldn't have worked properly on failure anyway,
since it would jump back to the exit label.

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 9be76f0..9378f2f 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -4613,9 +4613,6 @@
     mbedtls_endpoint_free( &client, NULL );
     mbedtls_endpoint_free( &server, NULL );
 
-    mbedtls_psa_get_stats( &stats );
-    TEST_ASSERT( stats.empty_slots == MBEDTLS_PSA_KEY_SLOT_COUNT );
-
     USE_PSA_DONE( );
 }
 /* END_CASE */