refactor: use GLib.find_program_in_path()

Use the more efficient built-in for checking if a program is in
the PATH.

appIcons.js

@@ -1833,7 +1833,7 @@ export const MyShowAppsIconMenu = class extends PopupMenu.PopupMenu {
 
     // Only add menu entries for commands that exist in path
     _appendItem(info) {
-        if (Utils.checkIfCommandExists(info.cmd[0])) {
+        if (GLib.find_program_in_path(info.cmd[0])) {
             let item = this._appendMenuItem(_(info.title));
 
             item.connect('activate', function() {

utils.js

@@ -893,28 +893,3 @@ export const drawRoundedLine = function(cr, x, y, width, height, isRoundLeft, is
         cr.setSource(stroke);
     cr.stroke();
 }
-
-/**
- * Check if an app exists in the system.
- */
-var checkedCommandsMap = new Map();
-
-export function checkIfCommandExists(app) {
-    let answer = checkedCommandsMap.get(app);
-    if (answer === undefined) {
-        // Command is a shell built in, use shell to call it.
-        // Quotes around app value are important. They let command operate
-        // on the whole value, instead of having shell interpret it.
-        let cmd = "sh -c 'command -v \"" + app + "\"'";
-        try {
-            let out = GLib.spawn_command_line_sync(cmd);
-            // out contains 1: stdout, 2: stderr, 3: exit code
-            answer = out[3] == 0;
-        } catch (ex) {
-            answer = false;
-        }
-
-        checkedCommandsMap.set(app, answer);
-    }
-    return answer;
-}