Revert "Compress/Encrypt Blocks in the background (#1227)" (#1409)

This reverts commit b13b927.
This commit is being reverted because we have seen some crashes which
could be caused by it. We haven't been able to reproduce the crashes yet.

Related to #1389, #1388, #1387
Also, see https://discuss.dgraph.io/t/current-state-of-badger-crashes/7602

This commit had some conflicts. See PR description for details.

db2_test.go

@@ -670,13 +670,16 @@ func TestL0GCBug(t *testing.T) {
 	// Simulate a crash by not closing db1 but releasing the locks.
 	if db1.dirLockGuard != nil {
 		require.NoError(t, db1.dirLockGuard.release())
-		db1.dirLockGuard = nil
 	}
 	if db1.valueDirGuard != nil {
 		require.NoError(t, db1.valueDirGuard.release())
-		db1.valueDirGuard = nil
 	}
-	require.NoError(t, db1.Close())
+	for _, f := range db1.vlog.filesMap {
+		require.NoError(t, f.fd.Close())
+	}
+	require.NoError(t, db1.registry.Close())
+	require.NoError(t, db1.lc.close())
+	require.NoError(t, db1.manifest.close())
 
 	db2, err := Open(opts)
 	require.NoError(t, err)

options.go

@@ -176,7 +176,6 @@ func DefaultOptions(path string) Options {
 
 func buildTableOptions(opt Options) table.Options {
 	return table.Options{
-		TableSize:               uint64(opt.MaxTableSize),
 		BlockSize:               opt.BlockSize,
 		BloomFalsePositive:      opt.BloomFalsePositive,
 		LoadBloomsOnOpen:        opt.LoadBloomsOnOpen,