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/option.c b/src/option.c
index e5e78d8..c10687f 100644
--- a/src/option.c
+++ b/src/option.c
@@ -6532,7 +6532,7 @@
 	case PV_VSTS:	return (char_u *)&(curbuf->b_p_vsts);
 	case PV_VTS:	return (char_u *)&(curbuf->b_p_vts);
 #endif
-	default:	iemsg(_(e_get_varp_error));
+	default:	iemsg(e_get_varp_error);
     }
     // always return a valid pointer to avoid a crash!
     return (char_u *)&(curbuf->b_p_wm);