Bug 22049: (follow-up) Remove leftover variable

Bug 22049: (follow-up) Remove leftover variable

The $circControlBranch variable was originally set to be used to pick
the right dropbox branch. It was only used in MarkIssueReturned, to get
the right Koha::Calendar object. As this responsability was moved top to
the AddReturn caller, and the fact that _GetCircControlBranch is
actually used for fines rules, there's no use for it in this context.
And it was left on the previous patch as a mistake.

To test:
- Make sure the variable is not actually used:
  $ git grep '$circControlBranch'
=> SUCCESS: removed variable is not actually used.
- Sign off :-D

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>