Revert "Reland "Make rtc_base/refcount.h self contained, not including refcountedobject.h.""

This reverts commit bf6937a8e90f94ac0ae50a296574b9f262b0932f.

Reason for revert: Broke internal projects.

Original change's description:
> Reland "Make rtc_base/refcount.h self contained, not including refcountedobject.h."
> 
> This is a reland of b7239a9dc825ddb25dbc800aed3a065163b9a10e
> Original change's description:
> > Make rtc_base/refcount.h self contained, not including refcountedobject.h.
> > 
> > The refcount.h file doesn't depend on anything from
> > refcountedobject.h. The motivation of this change to make it possible
> > to add additional declarations to refcount.h, and include it from
> > refcountedobject.h.
> > 
> > Bug: webrtc:8270
> > Change-Id: I24f6131f471e675570968d00065ff9b1f55e3373
> > Reviewed-on: https://webrtc-review.googlesource.com/5760
> > Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> > Commit-Queue: Niels Moller <nisse@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#20106}
> 
> Bug: webrtc:8270
> Change-Id: I9738f6680ab52d0f43639a1a39175fdba5957681
> Reviewed-on: https://webrtc-review.googlesource.com/5840
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#20180}

TBR=kwiberg@webrtc.org,nisse@webrtc.org

Change-Id: I342b241f5bb707b59ccf2d15a1a5befecb53a52e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8270
Reviewed-on: https://webrtc-review.googlesource.com/7280
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20181}

test/encoder_settings.cc

@@ -15,7 +15,6 @@
 #include "modules/video_coding/codecs/h264/include/h264.h"
 #include "modules/video_coding/codecs/vp8/include/vp8.h"
 #include "modules/video_coding/codecs/vp9/include/vp9.h"
-#include "rtc_base/refcountedobject.h"
 #include "test/fake_decoder.h"
 
 namespace webrtc {