Make gitea serv use api/internal

[sapk]

In order to limit concurrent access to database (mostly for SQLite)

Related: #4848 #2040

[lafriks]

Git clone tests seems to fail now

[lunny]

2018

[sapk]

I have not much time until 2 weeks. I will look at tests since I test clone manually and it worked but I must have forget one corner case.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@aefeb8c). Click here to learn what that means.
The diff coverage is 37.25%.

@@           Coverage Diff            @@
##             master   #4886   +/-   ##
========================================
  Coverage          ?   37.5%           
========================================
  Files             ?     310           
  Lines             ?   45929           
  Branches          ?       0           
========================================
  Hits              ?   17226           
  Misses            ?   26232           
  Partials          ?    2471

Impacted Files	Coverage Δ
routers/private/key.go	20% <20%> (ø)
routers/private/internal.go	58.2% <57.44%> (ø)

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[sapk]

I found the stupid mistake I made. 😑
This PR should be good.

[lunny]

Both hooks command also need to use api/internal.

[sapk]

@lunny I will have to verify but hook seems to only use const in models and already use private (api/internal).
We could drop https://github.com/go-gitea/gitea/blob/master/cmd/hook.go#L69 that shouldn't be needed anymore but that will be in another PR.

[lunny]

@sapk Another PR to remove that is good.