Fix duplication prevention.
Fix the bug: Feeds from all vsites are displayed in every vsite.
Fix: Only prevent RSS URL to appear twice in the same vsite.
Revert "Fix: Only prevent RSS URL to appear twice in the same vsite."

This reverts commit e6297a764f2f67de06f6e8986e7c84930eb83372.
Remove all duplication prevention code.
Merge branch '3715'.
Merge branch 'SCHOLAR-3.x' into 3715
Merge SCHOLAR-3.x
Fix tests.
Add docs & Fix typing errors
remove unneeded function.
Merge pull request #3722 from openscholar/3715

Fix some bugs on OS Reader Import