Libcore: fix three openjdk-redirect.html links.

[Cherry-picked because it's a prerequisite for the subsequent CL]

{@docRoot} already ends with /, so these links started with //
and were interpreted by the browser as going to the hostname
openjdk-redirect.html.

This CL fixes the malformed links by dropping the extra '/'.

The follow-up CL will touch (among others) these same lines,
but by fixing these links first, the follow-up CL topic will
become a pure refactoring with no impact on the doc generation.

Bug: 129765390
Test: Treehugger

(cherry picked from commit 0e40051bd1b31af7ef153dd79e8934251de2170d)

Change-Id: I9af84ed751799142b3f8b8c5af8a70854e21272b
Merged-In: I9af84ed751799142b3f8b8c5af8a70854e21272b