Remove webrtc/base/scoped_ptr.h

BUG=webrtc:5520

NOTRY=True

Review-Url: https://codereview.webrtc.org/1942823002
Cr-Original-Commit-Position: refs/heads/master@{#12684}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 65fc62e9dd8a8716db625aaef76ab92f542ecc5a