Stop disabling explicit GC

The problem here is simple: when using direct buffers as in NIO, the JDK
relies on explict GC invocataions to trigger cleaning up direct buffers;
if such GCs do not occur and the direct buffer limit is reached, the JVM
will throw an out of memory exception. With explicit GCs disabled, the
JVM is neutered from explicitly cleaning up direct buffers in the act of
reserving a new direct buffer and instead relies on a GC occurring for
another reason. If such a GC never occurs, the JVM will OOM. This commit
removes disabling of explicit GCs. Note that these explicit GCs only
occur as a last ditch effort before going OOM when the JVM is trying to
reserve more direct memory. This is a known issue, see for example:
JDK-8142537.

Relates #25759

distribution/src/main/resources/config/jvm.options

@@ -39,9 +39,6 @@
 
 ## optimizations
 
-# disable calls to System#gc
--XX:+DisableExplicitGC
-
 # pre-touch memory pages used by the JVM during initialization
 -XX:+AlwaysPreTouch