topic-revset: update the revset to no longer build changectx
Atribute access is expensive, and changectx are very expensive to build, so we
skip these for better performance.
Before:
! wall 0.012195 comb 0.020000 user 0.020000 sys 0.000000 (best of 217)
After:
! wall 0.008816 comb 0.010000 user 0.010000 sys 0.000000 (best of 303)
(Before this changeset parent)
! wall 0.213261 comb 0.210000 user 0.210000 sys 0.000000 (best of 45)