steam: removed the 'extra_info' set

This set was originally introduced to make the secondary user summary
request togglable. This option defaults to true, which means *most*
users will never turn this setting off. Additionally, this setting is
needed for the game status updates of Steam Friends, which is one of
the major points to using Steam's chat interface.

There is not much practically in keeping an option around that bloats
the code by ~50 lines if it is likely to never be used.
steam: reduced user mode spam upon changing game statuses

Currently, it is assumed that a new personastate event means a friend's
state actually changed, however, this is not always the case. A
personastate event is dispatched if a friend joins or changes gamer
servers, and this information is not relevant during poll operations.
Additionally, a large sum of repeated personastate events are sent when
the actual Steam client connects.

Since a flag cannot be passed to imcb_buddy_status() like it can be with
away states, everything is handled within the plugin. This means the
plugin needs to ensure that the game status is not already defined.
steam-util: steam_util_tree_ins: hint size check as unlikely
steam-api: staticize local scope arrays

This should have been done *long* ago.
steam-api: steam_api_poll_cb: refactored event parsing
steam: removed away state related prpl functions

Currently, it does not appear to be possible to set an away state, so
there is no point in retaining the skeleton code for it.