Remove unused namespace

This patch removes newly added an unused namespace.

Bug: 1519029
Change-Id: I030eb3d2bc6e6ba8fb68575919aa8117090e64ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5331917


Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1267426}