Move eirage@ from histograms others/ OWNER to custom_tabs/

Remove myself from metrics reviewer of others/ folder since all
TrustedWebAcitivy histograms has been moved to custom_tabs/
(crrev.com/c/3293131)

Add myself to custom_tabs/ metrics reviewer.

Change-Id: I1e3ccb2e14aec891ca7f25c5dc862f9b68405b6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3307267
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/main@{#947060}

tools/metrics/histograms/metadata/custom_tabs/OWNERS

@@ -0,0 +1,5 @@
+per-file OWNERS=file://tools/metrics/histograms/metadata/METRIC_REVIEWER_OWNERS
+
+# Prefer sending CLs to the owners listed below.
+# Use chromium-metrics-reviews@google.com as a backup.
+eirage@chromium.org

tools/metrics/histograms/metadata/others/OWNERS

@@ -6,8 +6,6 @@ per-file histograms.xml=file://tools/metrics/histograms/metadata/METRIC_REVIEWER
 
 # For display, mouse, and input related histograms.
 zentaro@chromium.org
-# For the TrustedWebActivity.* histograms:
-eirage@chromium.org
 # For Conversions.* histograms:
 johnidel@chromium.org
 # For Compositor*, Gpu.*, Graphics* and Viz.* histograms: