libsass: fix runtime version

libsass: fix runtime version

The version.h should be generated from version.h.in. But there is
already a version.h file in source directory. When ${S} != ${B}, the
version.h is generated in build directory, and the original version.h in
source directory is not overwritten. However, the latter is used during
the build, resulting in a missing runtime version. Remove version.h from
source directory to ensure that the one in build directory is used
during the build.

Before the fix:
$ sassc --version
sassc: [NA]
libsass: [NA]
sass2scss: 1.1.1
sass: 3.5

After the fix:
$ sassc  --version
sassc: 3.6.2
libsass: 3.6.6
sass2scss: 1.1.1
sass: 3.5

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>