[Telemetry] Allow keyboard tester open on multiple navigation

Currently, telemetry extension API cannot reopen keyboard tester on
subsequent navigation since URL is never updated after keyboard test
close.

Ensure that the URL param of `showDefaultKeyboardTester` is deleted on
dialog close, which will allow future redirect to reopen.

BUG=b/342086246
TEST=manual test on DUT

Change-Id: I1c9a1b8eda199f20e4b746db36b5b71978daf0a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5552783
Reviewed-by: Kerker Yang <kerker@chromium.org>
Reviewed-by: Denny Huang <dennyh@google.com>
Commit-Queue: Ethan Cheng <yycheng@google.com>
Cr-Commit-Position: refs/heads/main@{#1307215}