Remove spurious MPI send/recvs in parallel detector code
Remove spurious MPI send/recvs in parallel detector code

This is to avoid sending to all processes which causes issues for large
process counts.

I beleive this is the last case in the code of doing all-to-all
communication with individual MPI_(I)SEND and MPI_(I)RECV calls to/from
all processes.

jrper/fluidity,jrper/fluidity,jrper/fluidity,jrper/fluidity,jrper/fluidity