Revert "Scan /proc/<pid>/cmdline for GC roots"
Revert "Scan /proc/<pid>/cmdline for GC roots"

This reverts commit 194e3374b89b8b2dec6296923877304bdb5c6ae2.
Checking the command line for GC roots means that

  $ nix-store --delete $path

will fail because $path is now a root because it's mentioned on the
command line.

ysangkok/nix,jcumming/nix,rowhit/nix,joelmo/nix,pikajude/nix,acowley/nix,gebner/nix,edolstra/nix,bennofs/nix,zimbatm/nix,edolstra/nix,ehmry/nix,layus/nix,vizanto/nix,rycee/nix,rycee/nix,ysangkok/nix,shlevy/nix,NixOS/nix,zimbatm/nix,acowley/nix,dezgeg/nix,vcunat/nix,joelmo/nix,ysangkok/nix,ttuegel/nix,zimbatm/nix,bennofs/nix,tchajed/nix,zimbatm/nix,gridaphobe/nix,aucampia/nix,bennofs/nix,offlinehacker/nix,joelmo/nix,pikajude/nix,dtzWill/nix,edolstra/nix,aucampia/nix,shlevy/nix,wmertens/nix,peti/nix,rycee/nix,offlinehacker/nix,peti/nix,jcumming/nix,layus/nix,wmertens/nix,vcunat/nix,layus/nix,bjornfor/nix,nbp/nix,wmertens/nix,garbas/nix,NixOS/nix,tchajed/nix,acowley/nix,offlinehacker/nix,peti/nix,gridaphobe/nix,nbp/nix,layus/nix,rowhit/nix,ttuegel/nix,rowhit/nix,pikajude/nix,shlevy/nix,gridaphobe/nix,gebner/nix,rycee/nix,NixOS/nix,dezgeg/nix,ehmry/nix,offlinehacker/nix,garbas/nix,puffnfresh/nix,edolstra/nix,shlevy/nix,aucampia/nix,rowhit/nix,bjornfor/nix,ttuegel/nix,jcumming/nix,peti/nix,rycee/nix,bjornfor/nix,nbp/nix,dtzWill/nix,gridaphobe/nix,bjornfor/nix,puffnfresh/nix,nbp/nix,bennofs/nix,tchajed/nix,tchajed/nix,dezgeg/nix,puffnfresh/nix,garbas/nix,vizanto/nix,dtzWill/nix,garbas/nix,gebner/nix,gebner/nix,vcunat/nix,NixOS/nix,ttuegel/nix,dtzWill/nix,NixOS/nix,aucampia/nix,ehmry/nix,acowley/nix,vcunat/nix,layus/nix,puffnfresh/nix,garbas/nix,jcumming/nix,wmertens/nix,shlevy/nix,dezgeg/nix,peti/nix,vizanto/nix,edolstra/nix,joelmo/nix,ehmry/nix,ehmry/nix,ehmry/nix,dtzWill/nix,dezgeg/nix,vizanto/nix