pfUI's Lua hooksecurefunc lived in pfUI.env and shadowed ClassicAPI's C
global for all pfUI code. Replace it with a thin pfUI.hooksecurefunc shim
that keeps the missing-target no-op our call sites rely on (ClassicAPI
errors on a nil target) and delegates the actual hook to _G.hooksecurefunc.
Migrated all 70 internal call sites (modules/libs/skins) to
pfUI.hooksecurefunc; bare hooksecurefunc now resolves to ClassicAPI's C
version everywhere. Dropped the unused prepend path and the orphaned
pfUI.hooks table.
Brues