Remove use of windows perf counters

The windows implementation currently use Microsoft Performance Counters to fetch information of the system, and these counters may be disabled (or non-working/corrupt) and in that case couchbase server may fail to start (depending on the error reported).

It is possible to replace the implementation using the performance counters with functionality using the process api.

The only thing we'll currently loose would be subtraction of "file cache" from the memory statistics, but given all the trouble we've had with sigar (and the fact that the implementation introduced in trinity for io stats taken from the same source) I'm not confident that it is correct and we should probably just report the file cache as memory in use).