Revert "Upstream middle click paste defaults to false"

This reverts commit 0ea64216809dba4e2a25b718d8f14dd11ff64e71.

Upstream reverted the default to 'middle click paste is enabled'

https://git.gnome.org/browse/gnome-settings-daemon/commit/?id=e204eddcdbfb9f8d722355fab1643330c7d10c25