vnode_if: Remove some branching around SDT probes in VOP wrappers

Now that SDT is implemented using hot-patching, SDT_PROBE* no longer
introduces a branch instruction, so the SDT_PROBES_ENABLED() check in
each VOP_*_APV() is not really worth preserving.

Reviewed by: olce, kib
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D50423