Kconfig.debug: drop GCC 5+ version check for DWARF5

Now that the minimum supported version of GCC is 5.1, we no longer need
this Kconfig version check for CONFIG_DEBUG_INFO_DWARF5.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>