Composer.Widget: Do not set double dot after 'From' label

We do not set double dots after the other labels so remove it for the
'From' label as well.
Therefore, adjust the .ui file to have the right label (with the
mnemonic underscore) and remove the adjustment of it in code.
3 jobs for fix/remove_double_dot_from_from_label in 22 minutes and 45 seconds (queued for 2 seconds)