Revert of Break peerconnection_jni.cc into multiple files, in "pc" directory. (patchset #6 id:100001 of https://codereview.webrtc.org/2992103002/ )

Reason for revert:
Borken in the internal projects.

Original issue's description:
> Break peerconnection_jni.cc into multiple files, in "pc" directory.
>
> This CL breaks peerconnection_jni.cc apart, into one file for each
> class. It also moves the methods for converting between C++/Java
> structs into "java_native_conversion.cc", and uses a consistent naming
> scheme ("JavaToNativeX, NativeToJavaX"). These files go into a new
> "pc" directory, of which deadbeef@ is added as an owner.
>
> It also moves some relevant files to the "pc" directory that belong
> there: ownedfactoryandthreads, androidnetworkmonitor_jni, and
> rtcstatscollectorcallbackwrapper. This directory is intended to hold
> all the files that deal with the PeerConnection API specifically, or
> related classes (like DataChannel, RtpSender, MediaStreamTrack) that
> are tied to it closely.
>
> deadbeef@webrtc.org is added as an owner of the new "pc" subdirectory.
>
> BUG=webrtc:8055
>
> Review-Url: https://codereview.webrtc.org/2992103002
> Cr-Commit-Position: refs/heads/master@{#19223}
> Committed: https://chromium.googlesource.com/external/webrtc/+/dd7d8f1b609d51bcf39e9585871967a694a856bb

TBR=magjed@webrtc.org,sakal@webrtc.org,deadbeef@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:8055

Review-Url: https://codereview.webrtc.org/2989323002
Cr-Commit-Position: refs/heads/master@{#19226}