core: Remove GetVmsByUserid

GetVmsByUseridQuery is not used anywhere in
the code, and hence should be removed.

This patch removes the following:
1. The GetVmsByUseridQuery class
2. The GetVmsByUserid constant representing
   it in VdcQueryType
3. The GetVmsByUseridParameters class which
   was only used by the removed query class.

Change-Id: I1ed4821fceb06fbce6ac3f4b3851d903637b3132
Signed-off-by: Allon Mureinik <amureini@redhat.com>