Revert "Add a fallback to which pkexec on Linux"

This reverts commit 0e933b77c3.

index.js

@@ -124,7 +124,9 @@ function LinuxBinary(instance, end) {
   // However, gksudo cannot run multiple commands concurrently.
   var paths = ['/usr/bin/kdesudo', '/usr/bin/pkexec'];
   function test() {
-    if (index === paths.length) return which();
+    if (index === paths.length) {
+      return end(new Error('Unable to find pkexec or kdesudo.'));
+    }
     var path = paths[index++];
     Node.fs.stat(path,
       function(error) {
@@ -138,17 +140,6 @@ function LinuxBinary(instance, end) {
       }
     );
   }
-  function which() {
-    // Operating system paths are not always predictable.
-    // Fallback to a best-effort search for pkexec.
-    Node.child.exec('which pkexec',
-      function(error, stdout, stderr) {
-        if (error) return end(new Error('Unable to find pkexec or kdesudo.'));
-        var path = stdout.toString('utf-8').trim(); // Remove trailing newline.
-        end(undefined, path);
-      }
-    );
-  }
   test();
 }