[11u] Remove unused isUseContainerSupport in CgroupV1Subsystem

src/java.base/linux/classes/jdk/internal/platform/cgroupv1/CgroupV1Subsystem.java

declares a private native method isUseContainerSupport() see:

https://github.com/openjdk/jdk11u-dev/blob/24fec25451a71df8ccf2510227c6286fb8f792ca/src/java.base/linux/classes/jdk/internal/platform/cgroupv1/CgroupV1Subsystem.java#L509

The 11u backport of JDK-8231111 moved this to CgroupsMetrics class. See:
https://github.com/openjdk/jdk11u-dev/commit/19f26f725fdc29ee0eb4e330a275134663933629#diff-43f63fd495a029da52a87cc35df770564f51688106f5f6373ac5f36848f3c62dR170

This is a result of an out-of-order backport of JDK-8250627 ahead of
JDK-8231111. The stray declaration of CgroupV1Subsystem.isUseContainerSupport() should get removed as it's unused.