Cleanup rewirer code a bit

Created by: eseliger

I went looking through the code for the changeset rewirer and found some minor things I felt like changing, so here's a PR that does that. I split the changes up in separate commits.

Created by: sourcegraph-bot

Notifying subscribers in CODENOTIFY files for diff 7b5a3c03b0ec8fedd57b5d0c9eb0970dc1c43942...8242078d02c4b5febfef7aa5c735c705ce83a890.

Notify	File(s)
@LawnGnome	enterprise/internal/campaigns/service_apply_campaign.go

Created by: codecov[bot]

Codecov Report

Merging #15075 into main will increase coverage by 0.06%. The diff coverage is 51.02%.

@@            Coverage Diff             @@
##             main   #15075      +/-   ##
==========================================
+ Coverage   52.40%   52.47%   +0.06%     
==========================================
  Files        1557     1606      +49     
  Lines       79617    80344     +727     
  Branches     7002     7051      +49     
==========================================
+ Hits        41727    42161     +434     
- Misses      34152    34387     +235     
- Partials     3738     3796      +58     

Flag	Coverage Δ
#go	52.40% <48.87%> (+0.01%)
#integration	30.40% <12.64%> (+0.05%)
#storybook	26.11% <60.07%> (+0.25%)
#typescript	52.65% <58.15%> (+0.20%)
#unit	34.22% <4.25%> (+0.11%)

Impacted Files	Coverage Δ
client/shared/src/search/parser/diagnostics.ts	100.00% <ø> (ø)
...ent/web/src/enterprise/codeintel/detail/backend.ts	0.00% <0.00%> (ø)
...lient/web/src/enterprise/codeintel/list/backend.ts	0.00% <0.00%> (ø)
client/web/src/enterprise/repo/settings/routes.tsx	35.29% <0.00%> (ø)
client/web/src/enterprise/site-admin/routes.ts	6.66% <0.00%> (ø)
client/web/src/repogroups/Android.tsx	100.00% <ø> (ø)
client/web/src/repogroups/Golang.tsx	100.00% <ø> (ø)
client/web/src/repogroups/Kubernetes.tsx	100.00% <ø> (ø)
client/web/src/repogroups/Python2To3.tsx	100.00% <ø> (ø)
client/web/src/repogroups/ReactHooks.tsx	100.00% <ø> (ø)
... and 142 more