Fix up unused variable/value warnings.

Generic changes:

- Genuinely unused variables (-Wunused-variable): delete
  them. Sometimes add a comment if the variable is for an extension of
  the code that isn't done yet.

- Variables that became unused due to commented-out
  code (-Wunused-variable): comment out their definitions. Dirty, but
  that's because commenting out code instead of deleting it is
  dirty.

  Many of these are due to commented-out printlines that should have
  been log messages that only get emitted at high verbosity level.

Specific changes:

- SpikeObject.cpp (-Wunused-value): move initialization of loop
  variable into first for loop clause to silence the warning.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>