Remove error-setting macros from JingleMediaRtp
Remove error-setting macros from JingleMediaRtp

Two were unused; one didn't really buy much, and because the same macro
appears in several other files, hitting ^] in Vim to find its definition
doesn't work so well.

mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble