treewide: remove = __splicedPackages

Now that `pkgs` is `__splicedPackages` on cross we can remove these
variables I set.

Assignments like `patchutils = pkgs.patchutils_0_3_3;` in
`all-packages.nix` cannot be removed because the `pkgs`
in `patchutils = pkgs.patchutils_0_3_3;` in `all-packages.nix` is coming from
this `pkgs:` https://www.github.com/NixOS/nixpkgs/blob/b6e486730fc875ec79a3dea0f1f46eaf9f6ffa9d/pkgs/top-level/all-packages.nix#L9
instead of the `pkgs` in `with pkgs;`

Author: Artturin

pkgs/development/beam-modules/default.nix

@@ -1,11 +1,10 @@
 {
   lib,
-  __splicedPackages,
+  pkgs,
   erlang,
 }:
 
 let
-  pkgs = __splicedPackages;
   inherit (lib) makeExtensible;
 
   # FIXME: add support for overrideScope

pkgs/development/interpreters/perl/default.nix

@@ -30,11 +30,7 @@ let
             }:
             let
               perlPackagesFun = callPackage ../../../top-level/perl-packages.nix {
-                # allow 'perlPackages.override { pkgs = pkgs // { imagemagick = imagemagickBig; }; }' like in python3Packages
-                # most perl packages aren't called with callPackage so it's not possible to override their arguments individually
-                # the conditional is because the // above won't be applied to __splicedPackages and hopefully no one is doing that when cross-compiling
-                pkgs = if stdenv.buildPlatform != stdenv.hostPlatform then pkgs.__splicedPackages else pkgs;
-                inherit stdenv;
+                inherit stdenv pkgs;
                 perl = self;
               };
 

pkgs/top-level/all-packages.nix

@@ -4089,11 +4089,7 @@ with pkgs;
 
   tldr-hs = haskellPackages.tldr;
 
-  tmuxPlugins = recurseIntoAttrs (
-    callPackage ../misc/tmux-plugins {
-      pkgs = pkgs.__splicedPackages;
-    }
-  );
+  tmuxPlugins = recurseIntoAttrs (callPackage ../misc/tmux-plugins { });
 
   tpm2-totp-with-plymouth = tpm2-totp.override {
     withPlymouth = true;
@@ -4311,9 +4307,7 @@ with pkgs;
   yarn-berry_4 = yarn-berry.override { berryVersion = 4; };
   yarn-berry_3 = yarn-berry.override { berryVersion = 3; };
 
-  yarn2nix-moretea = callPackage ../development/tools/yarn2nix-moretea {
-    pkgs = pkgs.__splicedPackages;
-  };
+  yarn2nix-moretea = callPackage ../development/tools/yarn2nix-moretea { };
 
   inherit (yarn2nix-moretea)
     yarn2nix
@@ -5015,7 +5009,6 @@ with pkgs;
   idrisPackages = recurseIntoAttrs (
     callPackage ../development/idris-modules {
       idris-no-deps = haskellPackages.idris;
-      pkgs = pkgs.__splicedPackages;
     }
   );