Bug 47857: Deprecate #mw-mf-searchForm, allow search term clearing

Previously when typing a search term a cross appeared that allowed you
to reset the value. This code seems to have been lying dormant

Take opportunity to rename clearlink to more meaningful clear
Bug: 47857

Change-Id: Ib3db61be25452c4b3eedb5e54756cfe0d144882a
Merge "Bug 47857: Deprecate #mw-mf-searchForm, allow search term clearing"