Cleanup redundant AsFixedBytes and FixedLength traits (#3131)

* no need for AsFixedBytes we can just use AsRef<[u8]>

* cleanup FixedLength trait

* revert this change for now

* fix store tests

* cleanup and fix tests after rebase

* fix tests

* update based on PR review
less hard-coded values now

* cleanup

chain/src/chain.rs

@@ -179,7 +179,6 @@ impl Chain {
 			"header",
 			"header_head",
 			false,
-			true,
 			ProtocolVersion(1),
 			None,
 		)?;
@@ -188,7 +187,6 @@ impl Chain {
 			"header",
 			"sync_head",
 			false,
-			true,
 			ProtocolVersion(1),
 			None,
 		)?;

chain/src/txhashset/bitmap_accumulator.rs

@@ -20,7 +20,7 @@ use croaring::Bitmap;
 
 use crate::core::core::hash::{DefaultHashable, Hash};
 use crate::core::core::pmmr::{self, ReadonlyPMMR, VecBackend, PMMR};
-use crate::core::ser::{self, FixedLength, PMMRable, Readable, Reader, Writeable, Writer};
+use crate::core::ser::{self, PMMRable, Readable, Reader, Writeable, Writer};
 use crate::error::{Error, ErrorKind};
 
 /// The "bitmap accumulator" allows us to commit to a specific bitmap by splitting it into
@@ -215,10 +215,10 @@ impl PMMRable for BitmapChunk {
 	fn as_elmt(&self) -> Self::E {
 		self.clone()
 	}
-}
 
-impl FixedLength for BitmapChunk {
-	const LEN: usize = Self::LEN_BYTES;
+	fn elmt_size() -> Option<u16> {
+		Some(Self::LEN_BYTES as u16)
+	}
 }
 
 impl DefaultHashable for BitmapChunk {}

chain/src/txhashset/txhashset.rs

@@ -60,7 +60,6 @@ impl<T: PMMRable> PMMRHandle<T> {
 		sub_dir: &str,
 		file_name: &str,
 		prunable: bool,
-		fixed_size: bool,
 		version: ProtocolVersion,
 		header: Option<&BlockHeader>,
 	) -> Result<PMMRHandle<T>, Error> {
@@ -69,8 +68,7 @@ impl<T: PMMRable> PMMRHandle<T> {
 		let path_str = path.to_str().ok_or(Error::from(ErrorKind::Other(
 			"invalid file path".to_owned(),
 		)))?;
-		let backend =
-			PMMRBackend::new(path_str.to_string(), prunable, fixed_size, version, header)?;
+		let backend = PMMRBackend::new(path_str.to_string(), prunable, version, header)?;
 		let last_pos = backend.unpruned_size();
 		Ok(PMMRHandle { backend, last_pos })
 	}
@@ -136,7 +134,6 @@ impl TxHashSet {
 			TXHASHSET_SUBDIR,
 			OUTPUT_SUBDIR,
 			true,
-			true,
 			ProtocolVersion(1),
 			header,
 		)?;
@@ -146,7 +143,6 @@ impl TxHashSet {
 			TXHASHSET_SUBDIR,
 			RANGE_PROOF_SUBDIR,
 			true,
-			true,
 			ProtocolVersion(1),
 			header,
 		)?;
@@ -162,7 +158,6 @@ impl TxHashSet {
 				TXHASHSET_SUBDIR,
 				KERNEL_SUBDIR,
 				false, // not prunable
-				false, // variable size kernel data file
 				version,
 				None,
 			)?;