refactor: ignore ForcePlaintext in saved messages chat

ForcePlaintext was used for Autocrypt Setup Message,
there is no need to support it in saved messages chat anymore.

.github/workflows/dependabot.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
       - name: Dependabot metadata
         id: metadata
-        uses: dependabot/fetch-metadata@v3.0.0
+        uses: dependabot/fetch-metadata@v2.4.0
         with:
           github-token: "${{ secrets.GITHUB_TOKEN }}"
       - name: Approve a PR

deltachat-ffi/deltachat.h

@@ -4973,17 +4973,6 @@ uint32_t        dc_msg_get_original_msg_id    (const dc_msg_t* msg);
  */
 uint32_t        dc_msg_get_saved_msg_id     (const dc_msg_t* msg);
 
-
-/**
- * Force the message to be sent in plain text.
- *
- * This API is for bots, there is no need to expose it in the UI.
- *
- * @memberof dc_msg_t
- * @param msg The message object.
- */
-void            dc_msg_force_plaintext        (dc_msg_t* msg);
-
 /**
  * @class dc_contact_t
  *

deltachat-ffi/src/lib.rs

@@ -4054,16 +4054,6 @@ pub unsafe extern "C" fn dc_msg_get_saved_msg_id(msg: *const dc_msg_t) -> u32 {
     })
 }
 
-#[no_mangle]
-pub unsafe extern "C" fn dc_msg_force_plaintext(msg: *mut dc_msg_t) {
-    if msg.is_null() {
-        eprintln!("ignoring careless call to dc_msg_force_plaintext()");
-        return;
-    }
-    let ffi_msg = &mut *msg;
-    ffi_msg.message.force_plaintext();
-}
-
 // dc_contact_t
 
 /// FFI struct for [dc_contact_t]

python/src/deltachat/message.py

@@ -254,10 +254,6 @@ class Message:
         """Quote setter."""
         lib.dc_msg_set_quote(self._dc_msg, quoted_message._dc_msg)
 
-    def force_plaintext(self) -> None:
-        """Force the message to be sent in plain text."""
-        lib.dc_msg_force_plaintext(self._dc_msg)
-
     @property
     def error(self) -> Optional[str]:
         """Error message."""

src/message.rs

@@ -1319,7 +1319,7 @@ impl Message {
     }
 
     /// Force the message to be sent in plain text.
-    pub fn force_plaintext(&mut self) {
+    pub(crate) fn force_plaintext(&mut self) {
         self.param.set_int(Param::ForcePlaintext, 1);
     }
 

src/mimefactory.rs

@@ -232,11 +232,7 @@ impl MimeFactory {
         if chat.is_self_talk() {
             to.push((from_displayname.to_string(), from_addr.to_string()));
 
-            encryption_pubkeys = if msg.param.get_bool(Param::ForcePlaintext).unwrap_or(false) {
-                None
-            } else {
-                Some(Vec::new())
-            };
+            encryption_pubkeys = Some(Vec::new());
         } else if chat.is_mailing_list() {
             let list_post = chat
                 .param