Remove the 'ios_use_webrtc' build flag hack.

build_overrides/webrtc.gni

Index: build_overrides/webrtc.gni
diff --git a/build_overrides/webrtc.gni b/build_overrides/webrtc.gni
index 9b6b1608ca8ec722dc93bcbd58f0e9f8e7e52471..c521db7faa31bff207e1d68bcf7d9369e78326b0 100644
--- a/build_overrides/webrtc.gni
+++ b/build_overrides/webrtc.gni
@@ -10,11 +10,3 @@ rtc_include_pulse_audio = false
 
 # Exclude internal ADM since Chromium uses its own IO handling.
 rtc_include_internal_audio_device = false
-
-declare_args() {
-  # TODO(dpranke): This is a hack needed to get iOS to build w/ a
-  # patched version of WebRTC so that we can access the xmllite
-  # library. Remove this once we've figured out how to get WebRTC building
-  # properly.
-  ios_use_webrtc = false
-}