webrtc: Remove duplicate declarations

This causes 'redefinition of typedef ...' errors on GCC 4.5.3
3 jobs for milloni-ct/gcc-4.5 in 7 minutes and 40 seconds (queued for 9 minutes and 40 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #52106
manifest

00:00:30

 
  Build
passed #52107
build fedora x86_64

00:04:20

 
  Full Builds
passed #52108
build android arm64 api28

00:02:48