address some clippy warning about numeric maxima

Author: dwrensha

capnp/src/message.rs

@@ -505,7 +505,7 @@ where
             self,
             ReaderOptions {
                 traversal_limit_in_words: None,
-                nesting_limit: i32::max_value(),
+                nesting_limit: i32::MAX,
             },
         )
     }

capnp/src/private/arena.rs

@@ -19,7 +19,6 @@
 // THE SOFTWARE.
 
 use core::slice;
-use core::u64;
 
 use crate::message;
 use crate::message::Allocator;

capnp/src/private/layout.rs

@@ -3194,7 +3194,7 @@ impl<'a> PointerBuilder<'a> {
                 self.segment_id,
                 self.cap_table.into_reader(),
                 self.pointer,
-                ::core::i32::MAX,
+                i32::MAX,
             )
         }
     }