Remove unnecessary lib fallbacks

literalExpression was added in Nixpkgs 21.11, getExe in 22.05.
The minimum supported lib version is 22.05, so these fallbacks are unnecessary.

modules/apps.nix

@@ -8,12 +8,7 @@ let
     mkTransposedPerSystemModule
     ;
 
-  getExe = lib.getExe or (
-    x:
-    "${lib.getBin x}/bin/${x.meta.mainProgram or (throw ''Package ${x.name or ""} does not have meta.mainProgram set, so I don't know how to find the main executable. You can set meta.mainProgram, or pass the full path to executable, e.g. program = "''${pkg}/bin/foo"'')}"
-  );
-
-  programType = lib.types.coercedTo derivationType getExe lib.types.str;
+  programType = lib.types.coercedTo derivationType lib.getExe lib.types.str;
 
   derivationType = lib.types.package // {
     check = lib.isDerivation;
@@ -56,7 +51,7 @@ mkTransposedPerSystemModule {
     description = ''
       Programs runnable with nix run `<name>`.
     '';
-    example = lib.literalExpression or lib.literalExample ''
+    example = lib.literalExpression ''
       {
         default.program = "''${config.packages.hello}/bin/hello";
       }

modules/overlays.nix

@@ -14,7 +14,7 @@ in
       # This eta expansion exists for the sole purpose of making nix flake check happy.
       apply = lib.mapAttrs (_k: f: final: prev: f final prev);
       default = { };
-      example = lib.literalExpression or lib.literalExample ''
+      example = lib.literalExpression ''
         {
           default = final: prev: {};
         }