Removed module `Database.Query.Join`

The module only contained one function actually used, `leftJoin3'`, so I
I redefined it inline where it was used, and removed the module.
4 jobs for 431-remove-dead-code in 60 minutes and 4 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Cabal
passed #16554
cabal

00:27:07

 
  Stack
passed #16555
stack

00:07:11

 
  Bench
manual #16556
allowed to fail manual
bench
 
  Test
passed #16557
test

00:25:45