GN: Include webrtc/api targets even if rtc_include_tests=false
GN: Include webrtc/api targets even if rtc_include_tests=false

The main purpose with the rtc_include_tests GN variable is to avoid
generating and compiling all the test targets.
Some of our examples have dependencies on the test headers in API,
so therefore this change is relaxing that condition.

BUG=webrtc:6828
NOTRY=True
TBR=ehmaldonado@webrtc.org,

Review-Url: https://codereview.webrtc.org/2725053008
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#16989}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a769ceba656eff1d12df82ef3058306cf948b215

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