RFR(XS): 6721425: JConsole Makefile clean rule is missing rm of generated Version.java

[Erik Gahlin]

Without this change a 'gmake clean' in the jdk/make/sun/jconsole 
directory does not properly clean up the build results.

Bug:
http://monaco.us.oracle.com/detail.jsf?cr=6721425
Webrev:
http://cr.openjdk.java.net/~egahlin/6721425/

Thanks
Erik