patch 9.0.1594: some internal error messages are translated

Problem:    Some internal error messages are translated.
Solution:   Consistently do not translate internal error messages.
            (closes #12459)
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 72e5e25..d724d52 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5119,7 +5119,7 @@
 
 	default:
 	    // should not be here :P
-	    siemsg(_(e_nfa_regexp_invalid_character_class_nr), class);
+	    siemsg(e_nfa_regexp_invalid_character_class_nr, class);
 	    return FAIL;
     }
     return FAIL;
@@ -7341,7 +7341,7 @@
     // Be paranoid...
     if (prog == NULL || line == NULL)
     {
-	iemsg(_(e_null_argument));
+	iemsg(e_null_argument);
 	goto theend;
     }