tools/gn: remove three unused functions from string_utils.h

git grep shows these functions have no callers anymore.

BUG=None
TEST=gn gen + gn_unittests
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1483343004

Cr-Original-Commit-Position: refs/heads/master@{#362516}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0814cd9120dc3b96cc99a430188f4e3c0d2e2201
2 files changed
tree: edcc8b059f52f2ffa7865e012ead0f22cb583e55
  1. tools/