git_sha1: simplify logic

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

bin/git_sha1_gen.py

@@ -47,10 +47,6 @@ args = parser.parse_args()
 
 git_sha1 = os.environ.get('MESA_GIT_SHA1_OVERRIDE', get_git_sha1())[:10]
 if git_sha1:
-    git_sha1_h_in_path = os.path.join(os.path.dirname(sys.argv[0]),
-                                      '..', 'src', 'git_sha1.h.in')
-    with open(git_sha1_h_in_path, 'r') as git_sha1_h_in:
-        new_sha1 = git_sha1_h_in.read().replace('@VCS_TAG@', git_sha1)
-        write_if_different(new_sha1)
+    write_if_different('#define MESA_GIT_SHA1 "git-' + git_sha1 + '"')
 else:
     write_if_different('')