Don't make temporary directories symlinks

`toolcache.extractTar` currently falls over when `ACTIONS_TEMP` contains
a symlink, and the runner no longer exists, so it's unlikely our
customers would be running with temporary directories that contain
symlinks.

lib/util.js

@@ -89,11 +89,7 @@ exports.getToolNames = getToolNames;
 // Mostly intended for use within tests.
 async function withTmpDir(body) {
     const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "codeql-action-"));
-    const realSubdir = path.join(tmpDir, "real");
-    fs.mkdirSync(realSubdir);
-    const symlinkSubdir = path.join(tmpDir, "symlink");
-    fs.symlinkSync(realSubdir, symlinkSubdir, "dir");
-    const result = await body(symlinkSubdir);
+    const result = await body(tmpDir);
     await (0, del_1.default)(tmpDir, { force: true });
     return result;
 }