Remove RefBase from InputListener interface

We don't need refbase for inputlisteners. Remove it, and switch to
references, which cannot be null. This way, we can avoid dereferencing
the pointers without checking for nullness.

Bug: 198472780
Test: atest inputflinger_tests
Change-Id: I2f469fd268472c7e78d36812353cff5c52a90163
diff --git a/services/inputflinger/reader/mapper/InputMapper.h b/services/inputflinger/reader/mapper/InputMapper.h
index d9adc0f..f1c0e5a 100644
--- a/services/inputflinger/reader/mapper/InputMapper.h
+++ b/services/inputflinger/reader/mapper/InputMapper.h
@@ -48,7 +48,7 @@
     inline const std::string getDeviceName() { return mDeviceContext.getName(); }
     inline InputReaderContext* getContext() { return mDeviceContext.getContext(); }
     inline InputReaderPolicyInterface* getPolicy() { return getContext()->getPolicy(); }
-    inline InputListenerInterface* getListener() { return getContext()->getListener(); }
+    inline InputListenerInterface& getListener() { return getContext()->getListener(); }
 
     virtual uint32_t getSources() = 0;
     virtual void populateDeviceInfo(InputDeviceInfo* deviceInfo);