Translate: remove --disable-translate flag

Today, the flag is not maintained well, and is not consistently checked
to invoke the translation feature.

For testing, the translate feature is automatically disabled when
the API Key is not used to compile chromium. This check is also rough,
but should work similarly.
See, https://codereview.chromium.org/1185703007

To disable the feature completely, PolicyList can overwrite the translate
setting. This should work as users disable the feature in chrome://settings.
See, https://www.chromium.org/administrators/policy-list-3#TranslateEnabled

BUG=n/a

Review-Url: https://codereview.chromium.org/2819813002
Cr-Commit-Position: refs/heads/master@{#466605}
7 files changed