992: Remove old, unused LB instrumentation data structures

[JacobDomagala]

Fixes #992

[JacobDomagala]

Moving the discussion from issue(#992 (comment)) to this PR:

It seems that only vt/src/vt/lb/migration/lb_migratable.h is used (HasMigrate struct is base struct for UntypedCollection) I suggest we either move the file or the HasMigrate struct declaration to vt/src/vt/vrt/collection* directory.

NOTE: There's mention of this interface in vt/src/vt/vrt/collection/types/migratable.h:91 together with explanation how it's supposed to be used. Not sure if we want to touch it, just wanted to point that out since there's @todo added to it.

What's your opinion @lifflander @PhilMiller

[codecov]

Codecov Report

Merging #1108 into develop will increase coverage by 0.41%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1108      +/-   ##
===========================================
+ Coverage    75.61%   76.03%   +0.41%     
===========================================
  Files          719      712       -7     
  Lines        27255    27101     -154     
===========================================
- Hits         20609    20606       -3     
+ Misses        6646     6495     -151     

Impacted Files	Coverage Δ
src/vt/vrt/collection/types/has_migrate.h	100.00% <ø> (ø)
src/vt/vrt/collection/types/untyped.h	100.00% <ø> (ø)
src/vt/event/event_holder.cc	66.66% <0.00%> (-2.09%)	⬇️
src/vt/worker/worker_group_omp.cc	0.00% <0.00%> (-1.39%)	⬇️
src/vt/sequence/seq_node.cc	85.71% <0.00%> (-0.07%)	⬇️
src/vt/trace/trace.cc	64.50% <0.00%> (-0.07%)	⬇️
src/vt/utils/demangle/demangle.cc	95.77% <0.00%> (-0.06%)	⬇️
src/vt/timing/timing.cc	100.00% <0.00%> (ø)
src/vt/group/group_info.cc	100.00% <0.00%> (ø)
src/vt/messaging/pending_send.cc	100.00% <0.00%> (ø)
... and 6 more

[cz4rs]

👍