remove broken and silly Loader.isjava1() test in MDC static constructor

[ceki]

The Loader.isJava1() test in org.apache.log4j.MDC is broken when run in JDK 9 or later. MDC incorrectly assumes that the runtime environment is Java 1.1 (not 11 but 1.1) and disables MDC functionality entirely.

[ceki]

Fixed in commit 86d356c