Summary:
- fetching the history of an svn project only worked sometimes
- trying to show a diff between versions lead to a crash
- displaying a diff from the annotation border lead to a crash

- remove UI files which are not used
- remove unused svncatjob and svncheckoutmetadatawidget

Test Plan:
- display history/log from vcs context menu entry
- display diff from history list
- display diff from annotation border
- fetch svn project using the assistant
- commit changes of an svn project

Reviewers: #kdevelop, mwolff

Reviewed By: #kdevelop, mwolff

Subscribers: mwolff, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D9956