Telephony: Fix CollectionIncompatibleType

Ensure the key type is correct.

Found by Errorprone.

Bug: 73288226
Test: atest TeleServiceTests
Change-Id: I828ca78658d01ed2b86966c2f0989f24941685ca
diff --git a/src/com/android/services/telephony/ImsConference.java b/src/com/android/services/telephony/ImsConference.java
index 3cf420a..dd74d28 100644
--- a/src/com/android/services/telephony/ImsConference.java
+++ b/src/com/android/services/telephony/ImsConference.java
@@ -758,7 +758,8 @@
 
         participant.removeConnectionListener(mParticipantListener);
         synchronized(mUpdateSyncRoot) {
-            mConferenceParticipantConnections.remove(participant.getUserEntity());
+            mConferenceParticipantConnections.remove(new Pair<>(participant.getUserEntity(),
+                    participant.getEndpoint()));
         }
         mTelephonyConnectionService.removeConnection(participant);
     }