treewide: Don't use envHook anymore

This commits needs a MAJOR audit as I oftentimes just guessed which of
`$hostOffset`, `$targetOffset`, or a fixed offset should be used.

pkgs/applications/science/math/R/setup-hook.sh

@@ -1,5 +1,7 @@
 addRLibPath () {
-    addToSearchPath R_LIBS_SITE $1/library
+    if [[ -d "$1/library" ]]; then
+        addToSearchPath R_LIBS_SITE "$1/library"
+    fi
 }
 
-envHooks+=(addRLibPath)
+addEnvHooks "$targetOffset" addRLibPath