ops.c: eliminate static variable y_current

This variable isn't stateful, and should be passed around instead.

Helped-By: Scott Prager <splinterofchaos@gmail.com>
Helped-By: Michael Reed <m.reed@mykolab.com>

src/nvim/ex_docmd.c

@@ -6487,7 +6487,7 @@ static void ex_operators(exarg_T *eap)
 
   case CMD_yank:
     oa.op_type = OP_YANK;
-    (void)op_yank(&oa, FALSE, TRUE);
+    (void)op_yank(&oa, true);
     break;
 
   default:          /* CMD_rshift or CMD_lshift */