Remove webrtc_tests.
Remove webrtc_tests.

This target is just confusing, since it runs essentially random tests
out of the test binaries it's depending on. This CL makes the top
GN file structured like Chromium's is.

A possible secondary function is to act as a link test (maybe to catch
twice-defined symbols etc), but that seems highly speculative.

Bug: None
Change-Id: Ic8a36ffe96408312e602a58f8806b0694fedaad6
Reviewed-on: https://webrtc-review.googlesource.com/27380
Commit-Queue: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Reviewed-by: Oleh Prypin <5baa3e04f9bd6ba7a2a4b56625a3c84f19237cdb@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21028}
ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc