Make the decryptAscii helper function, in src/core/type1_parser.js, slightly more efficient

By slicing the Uint8Array directly, rather than using the prototype and a `call` invocation, the runtime of `decryptAscii` is decreased slightly (~30% based on quick logging).
The `decryptAscii` function is still less efficient than `decrypt`, however ASCII encoded Type1 font programs are sufficiently rare that it probably doesn't matter much (we've only seen *two* examples, issue 4630 and 11740).

src/core/type1_parser.js

@@ -437,7 +437,7 @@ var Type1Parser = (function Type1ParserClosure() {
         r = ((value + r) * c1 + c2) & ((1 << 16) - 1);
       }
     }
-    return Array.prototype.slice.call(decrypted, discardNumber, j);
+    return decrypted.slice(discardNumber, j);
   }
 
   function isSpecial(c) {