Remove suppression of removed clippy lint

    warning: lint `clippy::filter_map` has been removed: this lint has been replaced by `manual_filter_map`, a more specific lint
      --> serde_derive/src/lib.rs:42:5
       |
    42 |     clippy::filter_map,
       |     ^^^^^^^^^^^^^^^^^^
       |
       = note: `#[warn(renamed_and_removed_lints)]` on by default

    warning: lint `clippy::filter_map` has been removed: this lint has been replaced by `manual_filter_map`, a more specific lint
      --> serde_derive/src/lib.rs:42:5
       |
    42 |     clippy::filter_map,
       |     ^^^^^^^^^^^^^^^^^^

Author: dtolnay

serde_derive/src/lib.rs

@@ -39,7 +39,6 @@
     clippy::checked_conversions,
     clippy::doc_markdown,
     clippy::enum_glob_use,
-    clippy::filter_map,
     clippy::indexing_slicing,
     clippy::items_after_statements,
     clippy::let_underscore_drop,