Update API docs for TelecomManager#endCall.

Make it clear that ending an emergency call is not possible with this
method.

Test: Compile; this is a docs change.
Bug: 132438333
Change-Id: I736b90e31723ee2055cedf16142c4d0f494bf49b
(cherry picked from commit 3acf511895d8d19d5f9189d0159ae1d677a89a42)
diff --git a/telecomm/java/android/telecom/TelecomManager.java b/telecomm/java/android/telecom/TelecomManager.java
index 29898ff..f8f0bfd 100644
--- a/telecomm/java/android/telecom/TelecomManager.java
+++ b/telecomm/java/android/telecom/TelecomManager.java
@@ -1305,6 +1305,9 @@
      * foreground call is ended.
      * <p>
      * Requires permission {@link android.Manifest.permission#ANSWER_PHONE_CALLS}.
+     * <p>
+     * Note: this method CANNOT be used to end ongoing emergency calls and will return {@code false}
+     * if an attempt is made to end an emergency call.
      *
      * @return {@code true} if there is a call which will be rejected or terminated, {@code false}
      * otherwise.