Drop usage_guest and usage_guest_nice from cpu input

Both fields are always zero on Delphix engines — we don't run guest VMs.
Confirmed by Craig Alder (support). usage_nice is kept as it is uncertain
whether it will always be zero.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dbshah12

telegraf/telegraf.base

@@ -29,6 +29,9 @@
   collect_cpu_time = false
   report_active = false
   fieldpass = ["usage*"]
+  # usage_guest and usage_guest_nice are always zero on Delphix engines —
+  # we don't run guest VMs. Dropping them saves two fields per interval.
+  fielddrop = ["usage_guest", "usage_guest_nice"]
 
 # Get mount point stats
 [[inputs.disk]]