fix bug user search API pagesize didn't obey ExplorePagingNum

[lunny]

Will fix #3731. This PR will remove the wrong default limit code on route since the SearchUsers have the codes.

[codecov-io]

Codecov Report

Merging #6579 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6579      +/-   ##
==========================================
+ Coverage   40.35%   40.37%   +0.01%     
==========================================
  Files         405      405              
  Lines       54279    54277       -2     
==========================================
+ Hits        21906    21913       +7     
+ Misses      29356    29346      -10     
- Partials     3017     3018       +1

Impacted Files	Coverage Δ
routers/api/v1/user/user.go	23.7% <ø> (+0.34%)	⬆️
models/repo_list.go	66.84% <0%> (-1.06%)	⬇️
routers/repo/view.go	42.07% <0%> (+0.99%)	⬆️
modules/log/event.go	65.98% <0%> (+1.52%)	⬆️
models/unit.go	14.28% <0%> (+14.28%)	⬆️

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[techknowlogick]

@lunny merged. Please backport 😃

[lunny]

@techknowlogick back port done.