Removing EXPAT_RELATIVE_PATH and rtc_relative_path.

I think this was previously used in libjingle but it is not
used in WebRTC.

BUG=webrtc:8082

Review-Url: https://codereview.webrtc.org/2999703002
Cr-Original-Commit-Position: refs/heads/master@{#19523}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cb2bbce4e1920c874c76dcfcc54d6c9922c4ea4d
2 files changed