Remove remaining variables related to incomplete frames.

Bug: webrtc:9378, webrtc:7408
Change-Id: I5b26f09a2da13906b421d0bcf615e721b66d4ce7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/190860
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32552}

sdk/objc/base/RTCEncodedImage.m

@@ -23,7 +23,6 @@
 @synthesize encodeFinishMs = _encodeFinishMs;
 @synthesize frameType = _frameType;
 @synthesize rotation = _rotation;
-@synthesize completeFrame = _completeFrame;
 @synthesize qp = _qp;
 @synthesize contentType = _contentType;