tools headers: Remove broken definition of __LITTLE_ENDIAN

The linux/kconfig.h file was copied from the kernel but the line where
with the generated/autoconf.h include from where the CONFIG_ entries
would come from was deleted, as tools/ build system don't create that
file, so we ended up always defining just __LITTLE_ENDIAN as
CONFIG_CPU_BIG_ENDIAN was nowhere to be found.

This in turn ended up breaking the build in some systems where
__LITTLE_ENDIAN was already defined, such as the androind NDK.

So just ditch that block that depends on the CONFIG_CPU_BIG_ENDIAN
define.

The kconfig.h file was copied just to get IS_ENABLED() and a
'make -C tools/all' doesn't breaks with this removal.

Fixes: 93281c4a

 ("x86/insn: Add an insn_decode() API")
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/YO8hK7lqJcIWuBzx@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>