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/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index bb567e2..7df3671 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -380,6 +380,7 @@
     }
     int32_t id = mAllocatedDisplayIDs.firstUnmarkedBit();
     mAllocatedDisplayIDs.markBit(id);
+    mDisplayData[id].connected = true;
     return id;
 }
 
@@ -392,6 +393,7 @@
         return BAD_INDEX;
     }
     mAllocatedDisplayIDs.clearBit(id);
+    mDisplayData[id].connected = false;
     return NO_ERROR;
 }