patch 8.2.5029: "textlock" is always zero

Problem:    "textlock" is always zero.
Solution:   Remove "textlock" and rename "textwinlock" to "textlock".
            (closes #10489)
diff --git a/src/errors.h b/src/errors.h
index c819729..4e02986 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -1458,8 +1458,7 @@
 EXTERN char e_illegal_register_name[]
 	INIT(= N_("Illegal register name"));
 #endif
-EXTERN char e_not_allowed_to_change_text_here[]
-	INIT(= N_("E578: Not allowed to change text here"));
+// E578 unused
 #ifdef FEAT_EVAL
 EXTERN char e_if_nesting_too_deep[]
 	INIT(= N_("E579: :if nesting too deep"));