Updates to StringSplit implementation

Updates to StringSplit implementation

Remove the deprecated StringSplit implementation. The header declarations and all external uses were already removed, but the actual implementation was not removed.

It was still used by SplitStringIntoKeyValuePairs which is now updated to use the new version.

Both the key/value splitter and the substring variants have been updated to avoid many intermediate copies.

Updates the name of a trim whitespace variant in string_util to match the header. This is currently unused but was provided for symmetry before.

Committed: https://crrev.com/ce0fbef478ffe95f41e76bf6e85ff6b0072002ba
Cr-Commit-Position: refs/heads/master@{#343286}

[brettw, 2015-08-13 18:09:40]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-13 18:10:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1291103002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1291103002/40001

[commit-bot: I haz the power, 2015-08-13 19:50:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-13 19:50:35]

Dry run: This issue passed the CQ dry run.

[sky, 2015-08-13 20:45:50]

LGTM

[brettw, 2015-08-13 22:04:33]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-08-13 22:05:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1291103002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1291103002/40001

[commit-bot: I haz the power, 2015-08-13 22:10:08]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-08-13 22:10:38]

Patchset 3 (id:??) landed as
https://crrev.com/ce0fbef478ffe95f41e76bf6e85ff6b0072002ba
Cr-Commit-Position: refs/heads/master@{#343286}