[11u] Remove ea from DEFAULT_PROMOTED_VERSION_PRE in OpenJDK 11u

When backporting JDK-8223464 to OpenJDK 11u, the value DEFAULT_PROMOTED_VERSION_PRE=ea was introduced in make/autoconf/version-numbers.
While the value itself is only used by Oracle builds at this point, it should be maintained the same way in all OpenJDK update releases. The value should only be 'ea' for major releases that are still in a pre-ga state.

Since OpenJDK 11 has already been released, the value should be empty there. This aligns with OpenJDK 16 where `ea` has been removed with JDK-8259794.