Revert "Add GetModifiedFiles() function to git_utils."

This reverts commit af1de867422c42855ae54ed3838c62ea445ea6b4.

After removing svndiff.py in
https://skia.googlesource.com/skia/+/70242ace3b2ed06b33ee5ea5c9ac3aedea89b194,
nobody uses this function anymore.

R=borenet@google.com

Review URL: https://codereview.chromium.org/655383002

py/utils/git_utils.py

diff --git a/py/utils/git_utils.py b/py/utils/git_utils.py
index e0bb6e0..fec79d7 100644
--- a/py/utils/git_utils.py
+++ b/py/utils/git_utils.py
@@ -89,12 +89,6 @@
                           'refs/heads/master']).rstrip()
 
 
-def GetModifiedFiles():
-  """Returns a list of locally modified files within the current working dir.
-  """
-  return shell_utils.run([GIT, 'ls-files', '-m']).splitlines()
-
-
 def GetCurrentBranch():
   return shell_utils.run([GIT, 'rev-parse', '--abbrev-ref', 'HEAD']).rstrip()