Revert "Merge branch 'doc-fix-db-gem-install-instructions' into 'master'
"
Revert "Merge branch 'doc-fix-db-gem-install-instructions' into 'master'
"

This reverts commit 66d8ef1ad9d5952b7e7f026658f71aafc861950e, reversing
changes made to 6a8359f3d3be01af6f5b124b61af7ee1c77c17d0.

The `--with` option was added in Bundler 1.10 but in this case it
shouldn't even be needed: I've tested the original command locally and
the pg gem was installed, so I believe the user that opened the original
MR ran the wrong command (i.e. `sudo -u git -H bundle install --without
development test postgres --deployment` instead of `sudo -u git -H bundle
install --without development test mysql --deployment`.

See discussion at
https://gitlab.com/gitlab-org/gitlab-ce/commit/66d8ef1ad9d5952b7e7f026658f71aafc861950e
for more context.

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