Revert "Disable flaky presentation compiler test."

This reverts commit 8986ee4fd56c53d563165d992185c6c532f35790.

Scaladoc seems to work reliably for 2.11.x. We are using it in the IDE builds and haven't noticed any
flakiness, so we'd like to get reinstate this test.
Merge pull request #4027 from dragos/doc/reinstate-test

Revert "Disable flaky presentation compiler test."