Backport of #2143
This solves two bugs. One bug is that due to the JOIN with the
`forgejo_blocked_users` table, duplicated users were generated if a user
had more than one user blocked, this lead to receiving more than one
entry in the actions table. The other bug is that if a user blocked more
than one user, it would still receive a action entry by a
blocked user, because the SQL query would not exclude the other
duplicated users that was generated by the JOIN.
The new solution is somewhat non-optimal in my eyes, but it's better
than rewriting the query to become a potential perfomance blocker (usage
of WHERE IN, which cannot be rewritten to a JOIN). It simply removes the
watchers after it was retrieved by the SQL query.
(cherry picked from commit c63c00b39b)
