Bridging: Eliminate the unnecessary make channel compatible with bridge operation.

When a channel enters the bridging system it is first made compatible with
the bridge and then the bridge technology makes the channel compatible
with the technology.  For all but the DAHDI native and softmix bridge
technologies the make channel compatible with the bridge step is an
effective noop because the other technologies allow all audio formats.
For the DAHDI native bridge technology it doesn't matter because it is not
an initial bridge technology and chan_dahdi allows only one native format
per channel.  For the softmix bridge technology, it is a noop at best and
harmful at worst because the wrong translation path could be setup if the
channel's native formats allow more than one audio format.

This is an intermediate patch for a series of patches aimed at improving
translation path choices.

* Removed code dealing with the unnecessary step of making the channel
compatible with the bridge.

ASTERISK-24841
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/4600/
........

Merged revisions 434424 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@434430 65c4cc65-6c06-0410-ace0-fbb531ad65f3