simplify src/transaction/bundlr.rs Data

[lispwisp]

This just simplifies:

rust-sdk/src/transaction/bundlr.rs

Lines 18 to 22 in eca121d

	enum Data {
	None,
	Bytes(Vec<u8>),
	Stream(Pin<Box<dyn Stream<Item = anyhow::Result<Bytes>>>>),
	}

to this

rust-sdk/src/transaction/bundlr.rs

Line 21 in a0789d0

type Data = Option<Pin<Box<dyn Stream<Item = anyhow::Result<Bytes>>>>>;