Remove freeswitch.serial from fscomm/conf

freeswitch.serial is used by ZRTP as a ZID, so it should not be shared
between systems and definitely should not be distributed as a default
value by us.
Remove autogenerated file from tree

This file is specifically ignored by our .gitignore.  Brian added this
ignore on 2013-06-06 but neglected to remove the file.  I've now
bulid-tested without the file to be sure that it is indeed generated
correctly and so can be removed safely.
Improve our .gitignore files

Avoid ignoring files actually in our tree, and ignore some generated
files that were not being ignored previously.