Simplify allocation strategy for now

Not having `unsafe_no_drop_flag` caused some weirdness with optimizing buffers
and bytes. For now, remeove it.

test/test_append.rs

@@ -1,5 +1,4 @@
 use bytes::{Buf, MutBuf, AppendBuf};
-use bytes::alloc::Pool;
 
 #[test]
 pub fn test_initial_buf_empty() {
@@ -29,8 +28,10 @@ pub fn test_initial_buf_empty() {
     }
 }
 
+/*
 #[test]
 pub fn test_append_buf_from_pool() {
+    use bytes::alloc::Pool;
     let pool = Pool::with_capacity(2, 256);
 
     // Run in a loop a bunch in hope that if there is a memory issue, it will
@@ -58,3 +59,4 @@ pub fn test_append_buf_from_pool() {
         assert_eq!(dst, b"hello world");
     }
 }
+*/