Remove redundant webrtc:: prefixes in modules/desktop_capture

Created by
tools_webrtc/remove_extra_namespace.py --namespace webrtc

and manual adjustments.

This CL was uploaded by git cl split.

R=eshr@webrtc.org

No-IWYU: Refactoring
Bug: webrtc:42232595
Change-Id: If17c8431754579f5da8c82f219dedaa83e81d64a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/396169
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Auto-Submit: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#44892}