Remove --add-opens java.base/java.lang=ALL-UNNAMED from the JVM arguments used in our JDK11 integration tests

We had to add it in HSEARCH-3238, but ideally we should not have to use any add-opens.

See https://github.com/easymock/easymock/issues/235 in particular.

We will be able to remove it if:

• EasyMock fixes https://github.com/easymock/easymock/issues/235, for example by moving from cglib to bytebuddy

• OR EasyMock starts defining module dependencies and we run our tests in a modular environment, in which case we may be able to use --add-opens=java.base/java.lang=org.easymock instead, which is significantly better.

• OR we move from EasyMock to Mockito