fortify: remove `pragma diagnostic error` from tests

This was necessary because we weren't doing -Werror=fortify-source
everywhere. As of I2715ea411ef067f801534dab4d306fef5431f290, we should
be doing this.

Bug: 131861088
Test: mma
Change-Id: I00d499938ae24c3870760470576d6be603fbecd1
diff --git a/tests/clang_fortify_tests.cpp b/tests/clang_fortify_tests.cpp
index 2838ab2..018880f 100644
--- a/tests/clang_fortify_tests.cpp
+++ b/tests/clang_fortify_tests.cpp
@@ -69,7 +69,6 @@
 #define SOMETIMES_CONST volatile
 #else
 #define SOMETIMES_CONST const
-#pragma clang diagnostic error "-Wfortify-source"
 #endif
 
 #include <err.h>