Stop publishing default admin console credentials

AXIS2-6069 emptied the credentials in the configs the binary distribution
uses, but two published files kept admin/axis2: conf/axis2.xml inside the
axis2-webapp WAR, and axis2_default.xml inside axis2-kernel.jar, which is the
classpath fallback every configurator uses when no axis2.xml is found. Both
gave /axis2-admin a known login, and that console can upload services. Empty
both; the admin console tests now inject credentials into their unpacked copy
of the WAR instead.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>