The option 'default_host' for ejabberd_http was added years ago
in commit 7d623d5. However it was problematic and the usage was
removed in commit 83c291c. It's time to remove its last forgotten bits.
Conversion functions used by ej2sql module was not updated after change
that did allow storing multiple passwords per user, which made us skip
passwords that were updated to new format, this fixes this problem.
This fixes issue #4391