Separate wallcycle responsibilities

Separate wallcycle responsibilities

Collecting cycle counts, scaling them by thread count, summing them
over ranks, and printing the results are responsibilities worth
separating. This commit removes several fields from gmx_wallcycle
that don't relate to collecting cycle counts.

Specifically,
* the summation code no longer handles scaling by thread
  count, for which there is a new function.
* the summation code returns the summed cycle counts for printing,
  rather than keep it in the cycle-counting struct

Noted TODOs regarding
* the way ewcWAIT_GPU_NB_L is being used for load-balancing and
  never reporting, so should have a different implementation.
* reducing haveInvalidCount at the same time as counter summation
  has been buggy and is needless complexity
* wallcycle_sum needs to return both rank-0 and global data in
  a way that makes more clear how they should be used
* that finish_run can be cleaned up and move back to runner.cpp
* that scaling counters by thread counts should be the
  responsibility of the code that opened the counting region

Also, removed unused field from wallcc_t

Change-Id: Ieefdb3118c5de539debc3a48426fc0461182f5fe