Delete chrome://domain-reliability-internals debug UI.

This debug WebUI does not have any corresponding OWNERS files, and

1) even after trying to find people who are still interested in it
   based on git history, could not find any.
2) has not received any updates since it originally landed in 2014
   at https://codereview.chromium.org/357103002
3) the only modifications since are part of general horizontal changes
   (both in C++ and in frontend code)
4) Looking at histograms, there don't see to be any usage either.

Based on the above it seems reasonable to delete for now, and if
someone notices its absence and wants to keep it, we can re-instate
it with proper OWNERS files moving forward.

Bug: 1316438
Change-Id: I0b4816f767911cc323b195577b180ce4b55449d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3705920
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1014257}