Do not build rtp_generator in Chromium builds.
Do not build rtp_generator in Chromium builds.

This tool is only needed for WebRTC standalone so there is no need to
build it on Chromium trybots (if we want to do that, we need to
explicitly link against the Chromium's TQ implementation).

[1] - https://cs.chromium.org/chromium/src/third_party/webrtc_overrides/BUILD.gn?l=114-124&rcl=3514203635d4f5c2d660784dd3007f1018c9af88

Bug: None
Change-Id: Ib75204205717637e6b9b4320deaad5221ce35692
Reviewed-on: https://webrtc-review.googlesource.com/c/121405
Reviewed-by: Henrik Boström <106ab6647ddadbf38d6259e9d5ec4de77fa52c00@webrtc.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#26533}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc