Remove eroman@chromium.org from the metrics OWNER

All new chromium metrics OWNERS need to go through a training process
prior to being added as formal owners.

Bug: 1133371a
Change-Id: I9754559357078d74da73924406ede9c7435c06ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453342
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814724}

tools/metrics/histograms/histograms_xml/net/OWNERS

 # Networking Metrics Owners
 
 dschinazi@chromium.org
-eroman@chromium.org
 
 # If none of these reviewers are available, please send CLs to
 # <chromium-metrics-reviews@google.com>. See tools/metrics/histograms/OWNERS