[strong] Remove mjsunit/strong/use-strong-flag.js

[strong] Remove mjsunit/strong/use-strong-flag.js

It would force us to make mjsunit.js strong-compatible, and that's too much for
now (for the upcoming features) and would have a ripple effect on other
tests. Especially debug-script.js which unships harmony features would break.

R=rossberg@chromium.org
BUG=

Committed: https://crrev.com/7c15df8144ff1b164022a798fa38b5acb057a82f
Cr-Commit-Position: refs/heads/master@{#26694}

[rossberg, 2015-02-17 14:43:24]

lgtm

[rossberg, 2015-02-17 14:43:29]

The CQ bit was checked by rossberg@chromium.org

[commit-bot: I haz the power, 2015-02-17 14:44:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/930293002/1

[commit-bot: I haz the power, 2015-02-17 15:11:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-17 15:11:18]

Patchset 1 (id:??) landed as
https://crrev.com/7c15df8144ff1b164022a798fa38b5acb057a82f
Cr-Commit-Position: refs/heads/master@{#26694}