Remove temporary Git dependency from companion.txt (gwastro#5319)

Remove temporary Git dependency for PyPMC.

Author: GarethCabournDavies

companion.txt

@@ -15,8 +15,6 @@ https://github.com/willvousden/ptemcee/archive/master.tar.gz
 --extra-index-url https://download.pytorch.org/whl/cpu
 torch
 nessai>=0.11.0
-# TEMPORARY - REMOVE THIS ONCE PYPMC HAS A RELEASE v1.2.6
-git+https://github.com/pypmc/pypmc@dc5ff5f
 snowline
 
 # useful to look at PyCBC Live with htop