Remove verbose_name from hidden fields

verbose_name is unnecessary for hidden field.
Some verbose_name does not have much meaning
(it is just a mirror of form field name), but
it is marked as translated and such strings
are difficult to translate. To address this,
this commit cleans up verbose_name of hidden fields.

Change-Id: I14fc242f90ce22abe5a0517b44968c2a98f97f48
Closes-Bug: #1291548
Merge "Remove verbose_name from hidden fields"