configs/pool/critical-ld: move symlink to /usr/local/bin.

There is a bugfeature in pacman: NoExtract= files are removed on
upgrades (i. e. removed, but not extracted). So the previous /usr/bin
symlink got removed on each binutils upgrade.
system/essential/verbatim-files: systemd/{system,user}.conf: update for systemd-210.
configs/pool/common-*: move whatever is possible to system/essential/verbatim-files.

The latter location originally targets all files that are not meant to
be patched, and the former was invented just to handle site-specific
patches.
system/essential/verbatim-toplevel: netctl: add more wlan profiles.
configs/pool/common-mkinitcpio: mkinitcpio.conf: update HOOKS (use systemd hook).