Refactor InputHost and InputDriver

The host implementation of the HAL interface is largely done by the
InputDriver, so have it implement the opaque input_host_t type rather
than the InputHost itself. This allows the HAL interface to cast the
input_host_t pointer to an InputDriver pointer in order to implement
the host functionality.

Change-Id: I72de1e90eb6ee5e346c15707b8a6b793005bbccb
diff --git a/services/inputflinger/host/InputHost.h b/services/inputflinger/host/InputHost.h
index 42a66e0..eda4a89 100644
--- a/services/inputflinger/host/InputHost.h
+++ b/services/inputflinger/host/InputHost.h
@@ -26,15 +26,11 @@
 
 #include "InputDriver.h"
 
-// Declare a concrete type for the HAL
-struct input_host {
-};
-
 namespace android {
 
 class InputDriverInterface;
 
-class InputHostInterface : public input_host_t, public virtual RefBase {
+class InputHostInterface : public virtual RefBase {
 protected:
     InputHostInterface() = default;
     virtual ~InputHostInterface() = default;