Minor cleanups/fixes before virtual display refactoring

None of these should change behavior, except for removing some
incorrect log messages when using a virtual display.

- HWComposer::getAndResetReleaseFenceFd() checks the HWC version, so
  no need to do that in the DisplayDevice::onSwapBuffersCompleted().
  However, it should check that mFramebufferSurface is not NULL like
  it is for virtual displays.
- Comment that FramebufferSurface::dump() overrides the non-virtual
  ConsumerBase::dump(), and fix it so the right thing happens
  regardless of the static type of the pointer/reference the callee
  has. FramebufferSurface::dump() could be removed right now, but I'd
  need to bring it back in a later change.
- Use the right enum for validating display type ids.
- Don't try to send hotplug events for virtual displays.
- Mark virtual displays as connected so HWComposer::prepare() doesn't
  think something is wrong when it gets a non-NULL layer list.
- Remove unused FramebufferSurface methods.

Bug: 8384764
Change-Id: Id28a2f9be86b45f4bb7915fdf7752157035f4294
diff --git a/include/gui/ConsumerBase.h b/include/gui/ConsumerBase.h
index 49a764f..78a3608 100644
--- a/include/gui/ConsumerBase.h
+++ b/include/gui/ConsumerBase.h
@@ -69,10 +69,9 @@
     // ConsumerBase is connected.
     sp<BufferQueue> getBufferQueue() const;
 
-    // dump writes the current state to a string.  These methods should NOT be
-    // overridden by child classes.  Instead they should override the
-    // dumpLocked method, which is called by these methods after locking the
-    // mutex.
+    // dump writes the current state to a string. Child classes should add
+    // their state to the dump by overriding the dumpLocked method, which is
+    // called by these methods after locking the mutex.
     void dump(String8& result) const;
     void dump(String8& result, const char* prefix, char* buffer, size_t SIZE) const;