Suppress dep warnings in DD’s indent.t

I considered changing the code to suppress the warning, but:

• The warning only occurs before 5.12; the code is fine in
  later versions.
• By not changing the code I avoid the risk of sabotaging the test.
• By suppressing the warning conditionally based on perl version, we
  will still see future deprecations.

So this seems the least intrusive fix.
Stop using IV in pmop; remove workaround

See ticket #118055 for all the detail.  On systems where IV is bigger
than a pointer, the slab allocator messes things up because it only
provides pointer alignment.  If pmops have an IV field, we cannot
allocate them via slab on such systems.  Pmops actually don’t need
an IV, just a PADOFFSET.  So we can change them and remove the
workaround.

This is obviously not suitable for maint.