Remove `using` declaration for rtc::Buffer
Remove `using` declaration for rtc::Buffer

It interferes with a future refactoring, and isn't all that useful
anyway.

Bug: webrtc:9810
Change-Id: I46163d7921d39249615b7eea60306c598f13c128
Reviewed-on: https://webrtc-review.googlesource.com/c/103443
Reviewed-by: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Commit-Queue: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#24970}
ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc