Obsolete unused UseBsdPosixThreadCPUClocks

Summary

Obsolete the unused UseBsdPosixThreadCPUClocks flag.

Problem

The UseBsdPosixThreadCPUClocks was copied from Linux when the macOS port was done, but is actually unused on macOS/BSD.

Solution

Obsolete the UseBsdPosixThreadCPUClocks flag in JDK 16 and expire it in JDK 17.

Specification

Remove the flag definition from src/hotspot/os/bsd/globals_bsd.hpp:

-                                                                                \
-  /*  NB: The default value of UseBsdPosixThreadCPUClocks may be  */            \
-  /*  overridden in Arguments::parse_each_vm_init_arg.            */            \
-  product(bool, UseBsdPosixThreadCPUClocks, true,                               \
-          "enable fast Bsd Posix clocks where available")                       \

Add the flag to the obsoletion section of the special flag table:

+  { "UseBsdPosixThreadCPUClocks",          JDK_Version::undefined(), JDK_Version::jdk(16), JDK_Version::jdk(17) },