Chromium doesn't use the device managment code in webrtc/media
so we need a way to turn it off in order to eliminate Chromium's
src/third_party/libjingle/libjingle.gyp
BUG=webrtc:4256
NOTRY=True
TESTED=Trybots + successfully compiled with
GYP_DEFINES=include_internal_device_management=0 webrtc/build/gyp_webrtc
ninja -C out/Debug rtc_media
Review URL: https://codereview.webrtc.org/1693803002
Cr-Commit-Position: refs/heads/master@{#11816}