Moved call.h and most of api/call/* into call/

BUG=webrtc:6716

Review-Url: https://codereview.webrtc.org/2550273003
Cr-Commit-Position: refs/heads/master@{#15460}
diff --git a/webrtc/audio/BUILD.gn b/webrtc/audio/BUILD.gn
index bde074d..bfc2372 100644
--- a/webrtc/audio/BUILD.gn
+++ b/webrtc/audio/BUILD.gn
@@ -30,8 +30,8 @@
   deps = [
     "..:webrtc_common",
     "../api:audio_mixer_api",
-    "../api:call_api",
     "../base:rtc_base_approved",
+    "../call:call_interfaces",
     "../common_audio",
     "../modules/audio_device",
     "../modules/audio_processing",