Disable JS protobuf.

This prevents these imports [1] in the //third_party/protobuf/BUILD.gn.
They are problematic because WebRTC doesn't checkout //ui. While a
solution gets prepared, this CL unblocks the roll.

[1] = https://source.chromium.org/chromium/chromium/src/+/main:third_party/protobuf/BUILD.gn;l=8-13;drc=a87812bfda7d359447bfa383eeee2820926bd634

Bug: chromium:415076048
Change-Id: Idbaa5a7d9755f6e343d1d1c39d54e7943f1f8bfe
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/389981
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#44521}