Compilation warning fix for disass.el

* lisp/emacs-lisp/disass.el (disassemble-1): Remove a
string-as-unibyte that probably doesn't do anything, because the
string in question should be unibyte anyway.  If the assert fails,
revert the patch.

lisp/emacs-lisp/disass.el

@@ -168,7 +168,8 @@ OBJ should be a call to BYTE-CODE generated by the byte compiler."
       (fetch-bytecode obj)
       (setq bytes (aref obj 1)
 	    constvec (aref obj 2)))
-    (let ((lap (byte-decompile-bytecode (string-as-unibyte bytes) constvec))
+    (cl-assert (not (multibyte-string-p bytes)))
+    (let ((lap (byte-decompile-bytecode bytes constvec))
 	  op arg opname pc-value)
       (let ((tagno 0)
 	    tmp