patch 8.2.3967: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/autocmd.c b/src/autocmd.c
index 4831ea8..862370f 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -911,7 +911,7 @@
 		if (STRNCMP(cmd, "++once", 6) == 0 && VIM_ISWHITE(cmd[6]))
 		{
 		    if (once)
-			semsg(_(e_duparg2), "++once");
+			semsg(_(e_duplicate_argument_str), "++once");
 		    once = TRUE;
 		    cmd = skipwhite(cmd + 6);
 		}
@@ -920,7 +920,7 @@
 		if ((STRNCMP(cmd, "++nested", 8) == 0 && VIM_ISWHITE(cmd[8])))
 		{
 		    if (nested)
-			semsg(_(e_duparg2), "++nested");
+			semsg(_(e_duplicate_argument_str), "++nested");
 		    nested = TRUE;
 		    cmd = skipwhite(cmd + 8);
 		}
@@ -929,7 +929,7 @@
 		if (STRNCMP(cmd, "nested", 6) == 0 && VIM_ISWHITE(cmd[6]))
 		{
 		    if (nested)
-			semsg(_(e_duparg2), "nested");
+			semsg(_(e_duplicate_argument_str), "nested");
 		    nested = TRUE;
 		    cmd = skipwhite(cmd + 6);
 		}