Delete unused CRX/XML of test_certificate_provider

Now that the test_certificate_provider is installed via
ExtensionForceInstallMixin, maintaining the .crx and the
update_manifest.xml files manually is not needed anymore.

Bug: 1090941
Change-Id: Ic76e722f580de5b03cfd5a06dfe5cfb89caeacdf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566819
Commit-Queue: Fabian Sommer <fabiansommer@chromium.org>
Auto-Submit: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Fabian Sommer <fabiansommer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832414}

chrome/test/data/extensions/test_certificate_provider/update_manifest.xml

-<?xml version='1.0' encoding='UTF-8'?>
-<!--
-  This update manifest points to the ./extension.crx file.
-  "mock.http" is a placeholder that gets substituted with the test server
-  address in runtime.
--->
-<gupdate xmlns='http://www.google.com/update2/response' protocol='2.0'>
-  <app appid='ecmhnokcdiianioonpgakiooenfnonid'>
-    <updatecheck
-        codebase='http://mock.http/extensions/test_certificate_provider/extension.crx'
-        version='1.0' />
-   </app>
-</gupdate>