Remove deprecated offsetvector comparison

Calling `cmp` on instances of `offsetvector` is deprecated because
`cmp` is gone in Python 3.

See lscsoft/glue!19.
12 jobs for deprecate-offsetvector-cmp in 29 minutes and 23 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Level0
passed #24954
level0:lal

00:05:14

 
  Level1
passed #24955
level1:lalframe

00:01:59

passed #24956
level1:lalmetaio

00:01:58

passed #24957
level1:lalsimulation

00:05:32

passed #24958
level1:lalxml

00:01:36

 
  Level2
passed #24959
level2:lalburst

00:02:17

passed #24960
level2:lalinspiral

00:05:20

passed #24961
level2:lalpulsar

00:03:50

passed #24962
level2:lalstochastic

00:02:09

 
  Level3
passed #24963
level3:laldetchar

00:02:14

passed #24964
level3:lalinference

00:06:51

 
  Level4
passed #24965
level4:lalapps

00:06:24