Revert "selenium: add new message banner test to user spec"

Revert "selenium: add new message banner test to user spec"

This reverts commit 6ca3e221d1b907f55462394f910f283bb3627cc9.
This is breaking CI for the Minerva skin and Echo as Echo changes how
this interaction works. When the browser test tries to locate the
div.usermessage it has moved so fails.

This test needs to be rewritten to take this into account.

On a side note, given usermessage is generated by all skins (and not
in core) there is a big argument to be made that this shouldn't be in
core but in the individual skins. MinervaNeue the mobile skin notably
does not use this class so this test would always fail on a mediawiki
instance which only uses the Minerva skin.

Bug: T185928
Change-Id: I43b6cf328aaf4a4fded0bb9746716c4cc9d8f364