jmx-dev RFR: 8235681: Remove unnecessary workarounds in UnixOperatingSystem.c

[Daniil Titov]

Please review a change that removes unnecessary workaround in UnixOperatingSystem.c.  

It looks as this workaround 

if (pticks->usedKernel < tmp.usedKernel) {
        kdiff = 0;
 }

was added to compensate a missed initialization of counters.jvmTicks that resulted in the new
counters being compared with the garbage when  get_cpuload_internal(...) was called for the first time.

This missed initialization was fixed in [3].

Mach5 tier1-tier3 and open/test/hotspot/jtreg/containers/docker tests successfully passed. 

[1] Webrev : http://cr.openjdk.java.net/~dtitov/8235681/webrev.01/
[2] Issue: https://bugs.openjdk.java.net/browse/JDK-8235681 
[3] https://bugs.openjdk.java.net/browse/JDK-8226575 

Thank you,
Daniil