kselftest/arm64: Remove spurious comment from MTE test Makefile

There's a stray comment in the MTE test Makefile which documents
something that's since been removed, delete it.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20230111-arm64-kselftest-clang-v1-6-89c69d377727@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>