Fix new clippy warnings

The latest Rust version added some clippy checks.

src/bin/decoder/y4m.rs

@@ -50,7 +50,7 @@ impl Decoder for y4m::Decoder<'_, Box<dyn Read>> {
         );
         f
       })
-      .map_err(|e| e.into())
+      .map_err(Into::into)
   }
 }
 

src/deblock.rs

@@ -1385,7 +1385,6 @@ pub fn deblock_filter_frame<T: Pixel>(
 }
 
 fn sse_optimize<T: Pixel>(fs: &mut FrameState<T>, blocks: &FrameBlocks, bit_depth: usize) {
-  assert!(MAX_LOOP_FILTER < 999);
   // i64 allows us to accumulate a total of ~ 35 bits worth of pixels
   assert!(
     fs.input.planes[0].cfg.width.ilog() + fs.input.planes[0].cfg.height.ilog()
@@ -1467,8 +1466,7 @@ pub fn deblock_filter_optimize<T: Pixel>(
             (q * 20723 + 16_242_526 + (1 << 22 >> 1)) >> 22
           },
         _ => {
-          assert!(false);
-          0
+          unreachable!()
         }
       },
       0,

src/encoder.rs

@@ -1977,7 +1977,7 @@ fn encode_partition_topdown<T: Pixel>(
         });
       }
     },
-    _ => { assert!(false); },
+    _ => unreachable!(),
   }
 
   if is_square && bsize.gte(BlockSize::BLOCK_8X8) &&

src/rdo.rs

@@ -1200,7 +1200,7 @@ pub fn rdo_partition_decision<T: Pixel>(
         }
       }
       _ => {
-        assert!(false);
+        unreachable!();
       }
     }