Revert "scripts/setlocalversion: git: Make -dirty check more robust"

This reverts commit 6147b1cf.

The reverted patch results in attempted write access to the source
repository, even if that repository is mounted read-only.

Output from "strace git status -uno --porcelain":

getcwd("/tmp/linux-test", 129)          = 16
open("/tmp/linux-test/.git/index.lock", O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, 0666) =
	-1 EROFS (Read-only file system)

While git appears to be able to handle this situation, a monitored
build environment (such as the one used for Chrome OS kernel builds)
may detect it and bail out with an access violation error. On top of
that, the attempted write access suggests that git _will_ write to the
file even if a build output directory is specified. Users may have the
reasonable expectation that the source repository remains untouched in
that situation.

Fixes: 6147b1cf

 ("scripts/setlocalversion: git: Make -dirty check more robust"
Cc: Genki Sky <sky@genki.is>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>