Don't use regexp

Although immediate motivation is byte compiler error in older Emacs
due to rx not supporting "literal" clause, it is also the case that we
need not use a regexp at all.

racket-hash-lang.el

@@ -403,17 +403,18 @@ Otherwise things like `racket-xp-mode' will report errors.
 IFF we add one, arrange for a write-back function to remove it.
 Note: `org-src--contents-for-write-back' strips text properties
 so we can't insert a propertized string to look for later."
-  (save-excursion
-    (goto-char (point-min))
-    (unless (looking-at-p (rx bol "#lang" (1+ " ") (literal lang-str) "\n"))
-      (let ((lang-line-str (concat "#lang " lang-str "\n")))
-        (insert lang-line-str)
-        (setq org-src--allow-write-back
-              (lambda ()
-                (save-excursion
-                  (goto-char (point-min))
-                  (when (looking-at-p (rx bol (literal lang-line-str)))
-                    (delete-region (point-min) (1+ (length lang-line-str)))))))))))
+  (let* ((lang-line-str (concat "#lang " lang-str "\n"))
+         (end-pos (1+ (length lang-line-str))))
+    (unless (string= (buffer-substring-no-properties (point-min) end-pos)
+                     lang-line-str)
+      (save-excursion
+        (goto-char (point-min))
+        (insert lang-line-str))
+      (setq org-src--allow-write-back
+            (lambda ()
+              (when (string= (buffer-substring-no-properties (point-min) end-pos)
+                             lang-line-str)
+                (delete-region (point-min) end-pos)))))))
 
 (defun racket--hash-lang-org-babel-execute (lang-str body params)
   "A basic way to run Racket programs using any #lang.