Several fixes to screen_capturer_mac.
Several fixes to screen_capturer_mac.

Make sure that the appropriate run loop source gets added/removed. More clean up
to remove unnecessary functions and suppress deprecated declaration warnings.

BUG=webrtc:6029

Review-Url: https://codereview.webrtc.org/2417603002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14615}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 73fdc317b21afc4c1468eb11202a8cf09eddb000

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk