Remove validate_boot_option_for_trusted_boot metric

This removes the timing metric "validate_boot_option_for_trusted_boot"
because the validate_boot_parameters_for_trusted_boot() function is
an internal function that is called by PXEBoot.validate() -- which
is handled by the "PXEBoot.validate" metric. We shouldn't be emitting
metrics for such short-lived, internal functions.

Change-Id: Iaaa573fc4f128d6c3e20faf9c94259b352874eb8

ironic/drivers/modules/pxe.py

@@ -338,7 +338,6 @@ def _get_volume_pxe_options(task):
     return pxe_options
 
 
-@METRICS.timer('validate_boot_option_for_trusted_boot')
 def validate_boot_parameters_for_trusted_boot(node):
     """Check if boot parameters are valid for trusted boot."""
     boot_mode = deploy_utils.get_boot_mode_for_deploy(node)

releasenotes/notes/remove-metric-pxe-boot-option-1aec41aebecc1ce9.yaml

@@ -0,0 +1,6 @@
+---
+other:
+  - |
+    Removes the software metric named ``validate_boot_option_for_trusted_boot``.
+    This was the timing for a short-lived, internal function that is already
+    included in the ``PXEBoot.validate`` metric.