Remove genesis_block lazy initialization

This commit contains a change to address issue #752

cargo test runs successfully.

src/lib.rs

@@ -231,9 +231,6 @@ extern crate async_trait;
 #[macro_use]
 extern crate bdk_macros;
 
-#[cfg(feature = "compact_filters")]
-extern crate lazy_static;
-
 #[cfg(feature = "rpc")]
 pub extern crate bitcoincore_rpc;