Remove expansion of '%' #584.

Remove expansion of '%' #584.

The % is often used in urls and in case of the x-hint-command those are
feed to :shellcmd and will be replaced by current URL. This made the
x-hint-command unusable on some search engines.
The expansion of % to the current URL also required to give the current
browser state to the expansion logic and to feed it to all callers of
this too. This bloated the code.
This patch removes the % expansion which was a redundant alternative to
$VIMB_URI.