Remove root dir from protoc.gypi include paths.
Remove root dir from protoc.gypi include paths.

This include directory doesn't seem to be needed and is causing
problems in some downstream projects.

NOTRY=True

Review URL: https://codereview.webrtc.org/1903553005

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#12445}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 40bebd3c11fbb2a30e80b922c39b9170975959b1

jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc