[CI] Remove the Openjdk 8 dependency

Summary:
This dependency was added to provide Teamcity support, however we don't
run Teamcity in our build containers. We still need a JDK for building
the JNI bindings, so let's use the debian default (Openjdk 11).

Test Plan: Run some CI builds.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7786