core: Remove GetVmPoolMapByVmPoolId

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

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

Change-Id: I26120323c99b3043321032d3c495dc7faed0a8b3
Signed-off-by: Allon Mureinik <amureini@redhat.com>