Remove assertions that prelude/executable-exists?

I'm in the midst of transitioning onto a few new tools.

My previous workflow just used `nix-env` to install *some* packages. I didn't
have a prescribed methodology for which packages I would install using `nix-env`
and which ones I would install using `sudo apt-get install`. Sometimes if a
package would be available in my aptitude repositories, I'd use that; other
times when it wasn't available I'd use `nix-env`. One complication about being
on gLinux intead of NixOS is that some packages (e.g. nixpkgs.terminator) is
available via `nix-env -iA nixpkgs.terminator`, but the installation won't
actually run on my gLinux. In these instances, I would install terminator from
the aptitude repositories.

Then @tazjin introduced me to his Emacs configuration that he builds using
Nix. What appealed to me about his built Emacs is that it worked as expected on
either a NixOS machine and on gLinux (and presumably on other non-NixOS machines
as well).

A setup towards which I'm working is to own one or a few NixOS machines whose
configurations are entirely managed with Nix. On devices like my work machines,
which cannot run NixOS, I can build as much of the software that I need using
Nix and attempt to minimize the ad hoc configuration either with shell scripts,
python, golang, or more Nix code... it's clear that I still don't have a clear
idea of how that part will work.

For now, I'm adopting nix, nix-env, lorri, direnv, and weening off of aptitude
as much as I can. Things are a bit messy, but my general trend feels
positive. Stay tuned for more updates.

emacs/.emacs.d/wpc/clipboard.el

@@ -19,9 +19,6 @@
 (require 'prelude)
 (require 'ivy-clipmenu)
 
-(prelude/assert (prelude/executable-exists? "clipmenu"))
-(prelude/assert (prelude/executable-exists? "clipmenud"))
-
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Library
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

emacs/.emacs.d/wpc/scrot.el

@@ -15,9 +15,6 @@
 (require 'clipboard)
 (require 'kbd)
 
-(prelude/assert
- (prelude/executable-exists? "scrot"))
-
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Library
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

emacs/.emacs.d/wpc/wpc-golang.el

@@ -12,9 +12,6 @@
 
 (require 'prelude)
 
-(prelude/assert (prelude/executable-exists? "goimports"))
-(prelude/assert (prelude/executable-exists? "godef"))
-
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Configuration
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

emacs/.emacs.d/wpc/wpc-ocaml.el

@@ -19,9 +19,6 @@
 (require 'prelude)
 (require 'f)
 
-(prelude/assert
- (prelude/executable-exists? "opam"))
-
 (defvar opam-user-setup "~/.emacs.d/opam-user-setup.el"
   "File for the OPAM Emacs integration.")
 

emacs/default.nix

@@ -6,7 +6,12 @@
 
 let
   utils = import ~/briefcase/utils;
-  emacsBinPath = pkgs.lib.strings.makeBinPath [ pkgs.terminator ];
+  emacsBinPath = pkgs.lib.strings.makeBinPath (with pkgs; [
+    scrot
+    clipmenu
+    ocaml
+    ocamlformat
+  ]);
   emacsWithPackages = (pkgs.emacsPackagesNgGen pkgs.emacs26).emacsWithPackages;
   wpcarrosEmacs = emacsWithPackages (epkgs:
     (with epkgs.elpaPackages; [