Fix renamed let_underscore_drop lint

    warning: lint `clippy::let_underscore_drop` has been renamed to `let_underscore_drop`
      --> src/lib.rs:23:5
       |
    23 |     clippy::let_underscore_drop,
       |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `let_underscore_drop`
       |
       = note: `#[warn(renamed_and_removed_lints)]` on by default

    warning: lint `clippy::let_underscore_drop` has been renamed to `let_underscore_drop`
     --> src/bin/run-emitter-test-suite.rs:8:5
      |
    8 |     clippy::let_underscore_drop,
      |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `let_underscore_drop`
      |
      = note: `#[warn(renamed_and_removed_lints)]` on by default

    warning: lint `clippy::let_underscore_drop` has been renamed to `let_underscore_drop`
     --> src/bin/run-parser-test-suite.rs:8:5
      |
    8 |     clippy::let_underscore_drop,
      |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `let_underscore_drop`
      |
      = note: `#[warn(renamed_and_removed_lints)]` on by default

src/bin/run-emitter-test-suite.rs

@@ -5,7 +5,6 @@
     clippy::cast_possible_wrap,
     clippy::cast_sign_loss,
     clippy::items_after_statements,
-    clippy::let_underscore_drop,
     clippy::missing_errors_doc,
     clippy::missing_safety_doc,
     clippy::ptr_as_ptr,

src/bin/run-parser-test-suite.rs

@@ -5,7 +5,6 @@
     clippy::cast_possible_wrap,
     clippy::cast_sign_loss,
     clippy::items_after_statements,
-    clippy::let_underscore_drop,
     clippy::missing_errors_doc,
     clippy::missing_safety_doc,
     clippy::too_many_lines

src/lib.rs

@@ -20,7 +20,6 @@
     clippy::fn_params_excessive_bools,
     clippy::if_not_else,
     clippy::items_after_statements,
-    clippy::let_underscore_drop,
     clippy::manual_range_contains,
     clippy::manual_swap,
     clippy::missing_panics_doc,