Use rustfmt::skip instead of cfg_attr

Currently we use `cfg_attr` to disable the formatter so that the
attribute can be on an expression.

There was a new lint introduced into nightly just recently that checks
cfg args, this `cfg_attr` usage triggers it.

Use `rustfmt::skip` instead and put it on the function because it
doesn't currently work on expressions.

Author: tcharding

examples/sign_multisig.rs

@@ -93,8 +93,8 @@ fn spending_transaction() -> bitcoin::Transaction {
     }
 }
 
+#[rustfmt::skip]
 fn list_of_three_arbitrary_public_keys() -> Vec<bitcoin::PublicKey> {
-    #[cfg_attr(feature="cargo-fmt", rustfmt_skip)]
     vec![
         bitcoin::PublicKey::from_slice(&[2; 33]).expect("key 1"),
         bitcoin::PublicKey::from_slice(&[

examples/verify_tx.rs

@@ -102,9 +102,9 @@ fn main() {
 }
 
 /// Returns an arbitrary transaction.
+#[rustfmt::skip]
 fn hard_coded_transaction() -> bitcoin::Transaction {
     // tx `f27eba163c38ad3f34971198687a3f1882b7ec818599ffe469a8440d82261c98`
-    #[cfg_attr(feature="cargo-fmt", rustfmt_skip)]
     let tx_bytes = vec![
         0x01, 0x00, 0x00, 0x00, 0x02, 0xc5, 0x11, 0x1d, 0xb7, 0x93, 0x50, 0xc1,
         0x70, 0x28, 0x41, 0x39, 0xe8, 0xe3, 0x4e, 0xb0, 0xed, 0xba, 0x64, 0x7b,