Cherrypick from git_tm-dev: Fixing broken {docroot} links

CP to resolve downstream merge conflicts.

Original description:

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docs: Fixing broken {docroot} links

Fixing a couple of broken links (that used the wrong docroot
syntax). No changes to code.

Staged to:

* go/dac-stage/reference/android/app/Service
* go/dac-stage/reference/kotlin/android/app/Service

Change-Id: Ib50be686bfdd142f6c5a0d0bfccc7b1b411d5d14
BUG: 252953726
TEST: [local docs build]