Remove obsolete version checks and compat utilities after min SDK was bumped up to N.

Test: Existing tests
PiperOrigin-RevId: 190508397
Change-Id: Ia5f33e45af1d1cc666fec5f43efa564b2b68c193
diff --git a/java/com/android/incallui/call/DialerCall.java b/java/com/android/incallui/call/DialerCall.java
index 2ce4550..9a7c653 100644
--- a/java/com/android/incallui/call/DialerCall.java
+++ b/java/com/android/incallui/call/DialerCall.java
@@ -1018,13 +1018,10 @@
    * <p>An external call is one which does not exist locally for the {@link
    * android.telecom.ConnectionService} it is associated with.
    *
-   * <p>External calls are only supported in N and higher.
-   *
    * @return {@code true} if the call is an external call, {@code false} otherwise.
    */
-  public boolean isExternalCall() {
-    return VERSION.SDK_INT >= VERSION_CODES.N
-        && hasProperty(CallCompat.Details.PROPERTY_IS_EXTERNAL_CALL);
+  boolean isExternalCall() {
+    return hasProperty(CallCompat.Details.PROPERTY_IS_EXTERNAL_CALL);
   }
 
   /**