Run tests with java.security.manager=allow on JDK23+ in Avatica

Remove use of Java SecurityManager in Avatica.

Running Avatica on JDK 23 (or JRE 23) we get the following runtime errors:

Caused by: java.lang.UnsupportedOperationException: getSubject is supported only if a security manager is allowed at java.base/javax.security.auth.Subject.getSubject(Subject.java:347) at org.apache.calcite.avatica.server.SubjectPreservingPrivilegedThreadFactory.newThread(SubjectPreservingPrivilegedThreadFactory.java:43) 

We were warned - the getSubject method has been deprecated since JDK 18. The deprecation did not cause a build failure, due to CALCITE-5136.

HADOOP-19212 is an issue with the same underlying cause.

The message "getSubject is supported only if a security manager is allowed" implies that another solution would be to enable a security manager (including during tests, and when Avatica is used in Calcite's tests). Should we consider that? If so, please change the case summary.