Remove unused import statement

This import is not used, our CI obviously does not warn for all feature
combinations.

bitcoin/src/blockdata/script/builder.rs

@@ -1,7 +1,5 @@
 // SPDX-License-Identifier: CC0-1.0
 
-#[cfg(feature = "bitcoinconsensus")]
-use core::convert::From;
 use core::default::Default;
 use core::fmt;