[TieredStorage] Remove the general-purposed TieredStorageWriter (#196)

#### Problem
tiered_storage/writer.rs was added when we planned to support multiple
tiers in the tiered-storage (i.e., at least hot and cold).  However, as we
changed our plan to handle cold accounts as state-compressed accounts,
we don't need a general purposed tiered-storage writer at this moment.


#### Summary of Changes
Remove tiered_storage/writer.rs as we currently don't have plans to develop cold storage.

#### Test Plan
Existing tiered-storage tests.

accounts-db/src/tiered_storage.rs

@@ -11,7 +11,6 @@ pub mod mmap_utils;
 pub mod owners;
 pub mod readable;
 mod test_utils;
-pub mod writer;
 
 use {
     crate::{

accounts-db/src/tiered_storage/writer.rs

@@ -1,63 +0,0 @@
-//! docs/src/proposals/append-vec-storage.md
-
-use {
-    crate::{
-        account_storage::meta::{StorableAccountsWithHashesAndWriteVersions, StoredAccountInfo},
-        accounts_hash::AccountHash,
-        storable_accounts::StorableAccounts,
-        tiered_storage::{
-            error::TieredStorageError, file::TieredStorageFile, footer::TieredStorageFooter,
-            TieredStorageFormat, TieredStorageResult,
-        },
-    },
-    solana_sdk::account::ReadableAccount,
-    std::{borrow::Borrow, path::Path},
-};
-
-#[derive(Debug)]
-pub struct TieredStorageWriter<'format> {
-    storage: TieredStorageFile,
-    format: &'format TieredStorageFormat,
-}
-
-impl<'format> TieredStorageWriter<'format> {
-    pub fn new(
-        file_path: impl AsRef<Path>,
-        format: &'format TieredStorageFormat,
-    ) -> TieredStorageResult<Self> {
-        Ok(Self {
-            storage: TieredStorageFile::new_writable(file_path)?,
-            format,
-        })
-    }
-
-    pub fn write_accounts<
-        'a,
-        'b,
-        T: ReadableAccount + Sync,
-        U: StorableAccounts<'a, T>,
-        V: Borrow<AccountHash>,
-    >(
-        &self,
-        accounts: &StorableAccountsWithHashesAndWriteVersions<'a, 'b, T, U, V>,
-        skip: usize,
-    ) -> TieredStorageResult<Vec<StoredAccountInfo>> {
-        let footer = TieredStorageFooter {
-            account_meta_format: self.format.account_meta_format,
-            owners_block_format: self.format.owners_block_format,
-            account_block_format: self.format.account_block_format,
-            index_block_format: self.format.index_block_format,
-            account_entry_count: accounts
-                .accounts
-                .len()
-                .saturating_sub(skip)
-                .try_into()
-                .expect("num accounts <= u32::MAX"),
-            ..TieredStorageFooter::default()
-        };
-
-        footer.write_footer_block(&self.storage)?;
-
-        Err(TieredStorageError::Unsupported())
-    }
-}