Auto merge of #24606 - bombless:doc-result, r=alexcrichton

Get rid of the confusion that what does "custom" mean in this context.

Author: bors

src/libcore/result.rs

@@ -727,8 +727,8 @@ impl<T, E: fmt::Debug> Result<T, E> {
     ///
     /// # Panics
     ///
-    /// Panics if the value is an `Err`, with a custom panic message provided
-    /// by the `Err`'s value.
+    /// Panics if the value is an `Err`, with a panic message provided by the
+    /// `Err`'s value.
     ///
     /// # Examples
     ///