TEST_BUG: remove -showversion from RMI test library subprocess mechanism

The RMI test library (jdk/test/java/rmi/testlibrary) has a convenience API (the JavaVM class) for launching a JVM subprocess. When starting the subprocess, it adds the -showversion option to the JVM command line and waits for the version output to arrive from the subprocess before returning to the caller. This mechanism was added because the original code unconditionally slept for two seconds before returning to the caller, in an attempt to delay the caller until the JVM subprocess was ready. The -showversion mechanism reduced the wait time if the JVM subprocess became ready sooner.

It turns out this is no longer necessary.

The two-second delay was insufficient to avoid race conditions. Callers that need to interact with the JVM subprocess have to have their own wait/retry logic anyway. Indeed, this is elsewhere in the RMI test library already (RMID.java, ActivationLibrary.java), and in fact all the RMI tests pass with the two-second sleep and showversion mechanism removed, even if an extra delay is added to the subprocess.

Thus the two-second delay and the -showversion mechanism can be removed entirely.