Disable use of libevent under Fuchsia.
Disable use of libevent under Fuchsia.

Bug: chromium:808287
Change-Id: I1c29c5f2d13ad06904724fd95d476b23ae7097ac
Reviewed-on: https://webrtc-review.googlesource.com/50520
Reviewed-by: Sergey Ulanov <8a30473e5cf3b93eac32943832fa7a9609291d70@chromium.org>
Reviewed-by: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Commit-Queue: Tommi <74a97831ec830b6e3846c6faa50560947ae01c68@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21994}
TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc