Bug 1486038: Enable webrtc in aarch64-windows builds. r=dminor

--HG--
extra : rebase_source : c29b7c4ebf6b2520e9d702f4d1475484e53fca30

browser/config/mozconfigs/win64-aarch64/common-win64

@@ -3,8 +3,5 @@
 ac_add_options --target=aarch64-windows-mingw32
 ac_add_options --host=x86_64-pc-mingw32
 
-# WebRTC is busted in various ways.
-ac_add_options --disable-webrtc
-
 # Accessibility doesn't work.
 ac_add_options --disable-accessibility