Fix for the multi-video create subtitles form

This form is put on the tasks page and the dashboard page.  If a video
already has it's primary audio language set, we don't want to let the
user change it.  However, readonly is the correct attribute to use,
since if we use disabled then the value doesn't get POSTed at all.
Flag subtitle languages as complete when we approve tasks (#1377)
Dont allow users to post-edit subtitles for tasks teams (#1188)
Fix selectbox for primary language.

Setting the readonly attribute to "false" enables it.  We need to
remove the attribute to make it not read-only.
Merge pull request #1384 from pculture/gh-1377

Gh 1377