[UI] Modals should not have vertical scroll bars, but all do.
Created by: cirosantilli
Looks bad, specially when it leads to double scroll bars when there are body scroll bars, which currently always happens because of: https://github.com/gitlabhq/gitlabhq/issues/7497
The scrollbar comes from Bootstrap setting .modal {overflow-y: scroll}, https://github.com/twbs/bootstrap/issues/7972 asks why, https://github.com/twbs/bootstrap/issues/9855 might imply things will be solved in 3.2.