Fix ListSubmodule git call.

Bug: 1475770

Change-Id: I26f758fb3cbd9ac217e6e0abb719e13d21feb61f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5214266
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

scm.py

@@ -462,7 +462,7 @@ class GIT(object):
         if not os.path.exists(os.path.join(repo_root, '.gitmodules')):
             return []
         config_output = GIT.Capture(
-            ['git', 'config', '--file', '.gitmodules', '--get-regexp', 'path'],
+            ['config', '--file', '.gitmodules', '--get-regexp', 'path'],
             cwd=repo_root)
         return [line.split()[-1] for line in config_output.splitlines()]