Revisit vmlinux-$ARCH.h requirement for kprobe_pwru.c

[brb]

Currently we include vmlinux.h for each arch we support. However, @dylandreimerink pointed out that we don't need to:

Technically you don't even need vmlinux headers at all, just types with only the fields you are accessing https://nakryiko.com/posts/bpf-core-reference-guide/#defining-own-co-re-relocatable-type-definitions