Implement new In-Call Service interface

Change-Id: I200af25f175430a0cdc41009b9f3e8fd35d8c834
(cherry picked from commit b1e8965c7a0705adc4a8c85a88e8d29eeaf319db)
diff --git a/src/com/android/telecomm/Call.java b/src/com/android/telecomm/Call.java
index 13f7917..c1c7eb4 100644
--- a/src/com/android/telecomm/Call.java
+++ b/src/com/android/telecomm/Call.java
@@ -746,14 +746,7 @@
     }
 
     boolean isActive() {
-        switch (mState) {
-            case ACTIVE:
-            case POST_DIAL:
-            case POST_DIAL_WAIT:
-                return true;
-            default:
-                return false;
-        }
+        return mState == CallState.ACTIVE;
     }
 
     Bundle getExtras() {