Enable -Wunused-lambda-capture warning
Enable -Wunused-lambda-capture warning

This should prevent some build errors downstream.
The warning is currrently disabled in Chromium:
https://cs.chromium.org/chromium/src/build/config/compiler/BUILD.gn?rcl=735aa36217a394455f70aad87e2c844053fd810a&l=1214
(see https://crbug.com/681136 for more info).

BUG=webrtc:7133
NOTRY=True

Review-Url: https://codereview.webrtc.org/2999403002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#19466}

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