refactor: rename repl_msg_by_error into replace_msg_by_error

This function has been named like this since it was a C function.
`repl` is unclear because it may stand for `reply`
as well as `replace`.

src/mimeparser.rs

@@ -1358,7 +1358,7 @@ impl MimeMessage {
         self.get_mailinglist_header().is_some()
     }
 
-    pub fn repl_msg_by_error(&mut self, error_msg: &str) {
+    pub fn replace_msg_by_error(&mut self, error_msg: &str) {
         self.is_system_message = SystemMessage::Unknown;
         if let Some(part) = self.parts.first_mut() {
             part.typ = Viewtype::Text;