Remove feature global code search from GitLab CE

[codescale]

Just recently we realized that it's not possible to enable Global Search for a GitLab CE.

Their admin docs actually also says so. That's why I think it should be mark like that in your comparison page :)

[codecov-io]

Codecov Report

Merging #4875 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4875      +/-   ##
==========================================
+ Coverage   37.21%   37.22%   +<.01%     
==========================================
  Files         305      305              
  Lines       45043    45043              
==========================================
+ Hits        16763    16767       +4     
+ Misses      25842    25841       -1     
+ Partials     2438     2435       -3

Impacted Files	Coverage Δ
models/repo_list.go	56.37% <0%> (-1.35%)	⬇️
models/repo_indexer.go	52.11% <0%> (+1.27%)	⬆️
modules/process/manager.go	81.15% <0%> (+4.34%)	⬆️

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