Remove outdated versions of StartsWith and EndsWith from string_util.cc
Remove outdated versions of StartsWith and EndsWith from string_util.cc

It seems that old versions of StartsWith and EndsWith are unused
and can be removed completely.

R=brettw
BUG=none

Review URL: https://codereview.chromium.org/1278973004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#342838}

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