Simplify flow chart

crates/matrix-sdk-crypto/src/types/events/utd_cause.rs

@@ -196,24 +196,22 @@ impl UtdCause {
      * Below is the flow chart we follow for deciding whether historical
      * UTDs are expected. This function starts at position `B`.
      *
-     * ```mermaid
-     * flowchart TD
-     * A{Is the message newer than the device?}
-     * A -- No --> B
-     * A -- Yes --> X
-     * B{Is there a backup on the server?}
-     * B -- No --> Y
-     * B -- Yes --> C
-     * C{Is backup working on this device?}
-     * C -- No --> D
-     * C -- Yes --> X
-     * D{Is this device verified?}
-     * D -- No --> Z
-     * D -- Yes --> X
+     * ```text
+     * A: Is the message newer than the device?
+     *   No -> B
+     *   Yes - Normal UTD error
      *
-     * X([Normal UTD error])
-     * Y([History is not available on this device])
-     * Z([You need to verify this device])
+     * B: Is there a backup on the server?
+     *   No -> History is not available on this device
+     *   Yes -> C
+     *
+     * C: Is backup working on this device?
+     *   No -> D
+     *   Yes -> Normal UTD error
+     *
+     * D: Is this device verified?
+     *   No -> You need to verify this device
+     *   Yes -> Normal UTD error
      * ```
      */
     fn determine_historical(crypto_context_info: CryptoContextInfo) -> UtdCause {