sdp: remove old workaround
sdp: remove old workaround

Removes an old workaround for a firefox issue that was fixed in 2014.

BUG=webrtc:3212

Change-Id: I3ad71e29249908d840474cf3ee99a094c9201f6d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178381
Reviewed-by: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Commit-Queue: Philipp Hancke <563b103f57dc2044b12822c2a7559aa15cb1c987@googlemail.com>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#31584}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc