Today JFR can use either operating system time source or RDTSC (on x86). When using RDTSC, there is a check for if the CPU supports `invariant TSC`. If the CPU has no such support, the OS timer is used, *unless* `-XX:+UseFastUnorderedTimeStamps` is used.

Modern Processors generally support `invariant TSC`, however sometime the support is removed when running in a virtual machine.

Running without `invariant TSC` has several drawbacks, a steady frequency is not guaranteed, nor is forward movement. If we remove support for this, timers will behave better, and we can also remove code for frequency detection that is in nature unsound, especially in user space where we do not control frequency scaling and CPU boost.

In addition to removing code paths for "variant" TSC, we should also document the flag UseFastUnorderedTimeStamps, and possibly even change the name.