Remove --enable-filemanager-mtp flag.

Remove --enable-filemanager-mtp flag.

It's now default and unlikely to be turned off.

BUG=407455
TEST=manually tested MTP works and about:flags doesn't have the entry for MTP.

Committed: https://crrev.com/0db57093f55bcbdfb3a02d65315b20cbf4d49162
Cr-Commit-Position: refs/heads/master@{#293098}

[kinaba, 2014-09-03 05:07:29]

kinaba@chromium.org changed reviewers:
+ hirono@chromium.org

[hirono, 2014-09-03 07:19:59]

lgtm

[kinaba, 2014-09-03 07:22:28]

The CQ bit was checked by kinaba@chromium.org

[commit-bot: I haz the power, 2014-09-03 07:23:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kinaba@chromium.org/533893003/1

[commit-bot: I haz the power, 2014-09-03 08:19:49]

Committed patchset #1 (id:1) as 93fae5bc254db15ba8b83979ca4786baa93a7d24

[commit-bot: I haz the power, 2014-09-10 03:24:26]

Patchset 1 (id:??) landed as
https://crrev.com/0db57093f55bcbdfb3a02d65315b20cbf4d49162
Cr-Commit-Position: refs/heads/master@{#293098}