nixos: default environment.homeBinInPath to false

This is a more sane default since we do not magically (without opt-in)
pull in binaries from `~/bin`. That is not really an expected behavior
for many users. Users that still want that behavior can now just flip
that switch.

nixos/modules/config/shells-environment.nix

@@ -122,7 +122,7 @@ in
       description = ''
         Include ~/bin/ in $PATH.
       '';
-      default = true;
+      default = false;
       type = types.bool;
     };