Simplify allocation strategy for now

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

src/lib.rs

@@ -13,7 +13,7 @@ pub mod alloc;
 
 pub use buf::{Buf, MutBuf, Source, Sink, ReadExt, WriteExt, Fmt};
 pub use buf::append::AppendBuf;
-pub use buf::block::{BlockBuf, NewBlock, BlockBufCursor};
+pub use buf::block::{BlockBuf, BlockBufCursor};
 pub use buf::byte::{ByteBuf, MutByteBuf};
 pub use buf::ring::RingBuf;
 pub use buf::take::Take;