Fixed the bug noted in issue mom-ocean#72 and excessive loop sizes noted in the
unresolved comments in a recent commit, and cleaned up other aspects of
MOM_hor_visc, mostly related to the code that is exercised when USE_GME=True.

 - Fixed the bug with the wrong arrays being used when ADD_LES_VISCOSITY=True
   that was noted in MOM6 issue mom-ocean#72.

 - Corrected some of the overly large loop extents that were noted in unresolved
   comments about MOM6 PR mom-ocean#65.

 - Only log USE_KH_BG_2D if a Laplacian viscosity is used.

 - Use extra calculations in the halos and marching in to avoid unnecessary halo
   updates in smooth_GME if there multiple smoothing passes.

 - Corrected the capitalization of some horizontal indices to follow the MOM6
   convention for indicating the horizontal staggering position.

 - Collected the post_data calls for diagnostics with use_GME with the other
   post data calls to collocate some of the potential inter-PE synchronization
   points.

 - Fixed the indentation of some expressions that were using less than 4 points
   for some continuation lines.

 - Eliminated several unused variables, and fused some loops to allow 2-d
   variables to be replaced with scalars.

  With this PR, answers can change when ADD_LES_VISCOSITY=True and there is a
Smagorinsky or Leith Laplacian viscosity and there is a nonzero background.
One run-time parameter is no longer logged if LAPLACIAN=false, so there are
changes to the MOM_parameter_doc files.  All answers in the MOM6-examples test
suite are bitwise identical.

  Minor code cleanup in response to the code review from Gustavo Marques.  In
particular, this introduces a roundoff-level answer changing code simplification
for code that is only exercised if USE_GME=True.  In all other cases the answers
are bitwise identical.