multi_buffer: Remove redundant buffer id field (#43459)

It is easy for us to get the two fields out of sync causing weird
problems, there is no reason to have both here so.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

Co-authored by: Antonio Scandurra <antonio@zed.dev>

crates/editor/src/test/editor_test_context.rs

@@ -490,11 +490,7 @@ impl EditorTestContext {
             );
             assert_eq!(
                 multibuffer_snapshot
-                    .text_for_range(Anchor::range_in_buffer(
-                        excerpt_id,
-                        snapshot.remote_id(),
-                        range.context.clone()
-                    ))
+                    .text_for_range(Anchor::range_in_buffer(excerpt_id, range.context.clone()))
                     .collect::<String>(),
                 expected_text,
                 "{}",
@@ -675,11 +671,7 @@ impl std::fmt::Display for FormatMultiBufferAsMarkedText {
             }
 
             let mut text = multibuffer_snapshot
-                .text_for_range(Anchor::range_in_buffer(
-                    *excerpt_id,
-                    snapshot.remote_id(),
-                    range.context.clone(),
-                ))
+                .text_for_range(Anchor::range_in_buffer(*excerpt_id, range.context.clone()))
                 .collect::<String>();
 
             let selections = selections