Why is this change required?
The flaky system test was due to the fact that we had to poll for the
user preferences interface page to reload after saving. However, this
turns out to be a bug on the user perferences interface page because the
page should only reload if the user has selected a new theme that is
different from the site's default but we were reloading the page for
users that did not have any user theme selected. Therefore there was an
unnecessary reload happening when saving other fields on the user
preferences interface page.
We were changing the user's user_option.bookmark_auto_delete_preference
to whatever they changed it to in the bookmark modal to use as default
for future bookmarks. However this was leading to a lot of confusion
since if you wanted to set it for one bookmark you had to remember to
change it back on the next one.
This commit removes that automatic functionality, and instead moves
the bookmark auto delete preference to User Preferences > Interface
in an explicit dropdown.
