This reverts commit 5a586f364c5d2b866d6a074eff7996f05585b7d5

This reverts merge request !3191

Support Golang subpackage fetching

Closes #13805

See merge request !3191

Fix importing PR's from GitHub when the source repo was removed

Closes #13847 
Closes gitlab-com/support-forum#584

See merge request !3172

Disallow blank (non-null) values for a Note's `line_code` attribute

It's unclear how these blank values got added, but GitLab.com had a few:

```
irb(main):002:0> Note.where("line_code IS NOT NULL AND line_code = ''").count
=> 439
```

We've added a migration to convert any existing records to use a NULL
value when blank, and updated Note to set blank values to nil before
validation.

See merge request !3118

It's unclear how these blank values got added, but GitLab.com had a few:

```
irb(main):002:0> Note.where("line_code IS NOT NULL AND line_code = ''").count
=> 439
```

We've added a migration to convert any existing records to use a NULL
value when blank, and updated Note to set blank values to nil before
validation.

Use a custom Devise failure app to handle unauthenticated .zip requests

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/12944

See merge request !2828

The OR condition for source_project_id/target_project_id leads to a
query plan that performs rather poorly on PostgreSQL due to the use of
sub-queries. Because Rails offers no easy alternative for this
particular problem we're forced to using a UNION for both conditions.
The resulting query performs much faster than just using an OR.