Remove unused config option

[MorrisJobke]

Found while looking through the code.

[codecov]

Codecov Report

Merging #9276 into master will decrease coverage by 2.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #9276      +/-   ##
============================================
- Coverage     54.01%   51.94%   -2.07%     
- Complexity    24075    25375    +1300     
============================================
  Files          1513     1607      +94     
  Lines         88690    95394    +6704     
  Branches       1394     1394              
============================================
+ Hits          47905    49557    +1652     
- Misses        40785    45837    +5052

Impacted Files	Coverage Δ	Complexity Δ
config/config.sample.php	0% <ø> (ø)	0 <0> (ø)	⬇️
.../tests/Unit/Collaboration/CommentersSorterTest.php	25.55% <0%> (-66.45%)	6% <0%> (ø)
apps/sharebymail/tests/SettingsTest.php	52.17% <0%> (-47.83%)	3% <0%> (ø)
lib/private/Security/RateLimiting/Limiter.php	55.55% <0%> (-44.45%)	5% <0%> (ø)
settings/Controller/GroupsController.php	68.33% <0%> (-31.67%)	9% <0%> (ø)
...b/private/App/AppStore/Fetcher/CategoryFetcher.php	69.23% <0%> (-30.77%)	1% <0%> (ø)
...ps/comments/tests/Unit/AppInfo/ApplicationTest.php	69.56% <0%> (-30.44%)	4% <0%> (ø)
apps/user_ldap/lib/Configuration.php	43.68% <0%> (-29.21%)	87% <0%> (ø)
lib/private/AvatarManager.php	71.42% <0%> (-28.58%)	4% <0%> (ø)
apps/encryption/lib/Command/EnableMasterKey.php	75% <0%> (-25%)	5% <0%> (ø)
... and 278 more