nodeinfo: drop static variable

nodeinfo: drop static variable

We were wasting time to malloc a copy of a constant string, then
copy it into static storage, for every call to nodeGetInfo.  At
least we were lucky that it was a constant source, and thus not
subject to even worse issues with one thread clobbering the static
storage while another was using it.  This gets rid of the waste,
by passing the string through the stack instead, as well as renaming
internal functions to better match our conventions.

* src/nodeinfo.c (sysfs_path): Delete.
(get_cpu_value, count_thread_siblings, parse_socket): Add
parameter, and rename...
(virNodeGetCpuValue, virNodeCountThreadSiblings)
(virNodeParseSocket): ... into a common namespace.
(cpu_online, parse_core): Inline into callers.
(linuxNodeInfoCPUPopulate): Update caller.
(nodeGetInfo): Drop a useless malloc.