Move bip-174 test out of examples and into tests

The `examples/psbt.rs` file isn't adding much value as an example, it is
just implementing tests against test vectors from the bip. Better to put
it in `tests` than in `examples`.

Author: tcharding

Cargo.toml

@@ -52,10 +52,6 @@ required-features = ["std"]
 name = "verify_tx"
 required-features = ["std"]
 
-[[example]]
-name = "psbt"
-required-features = ["std"]
-
 [[example]]
 name = "xpub_descriptors"
 required-features = ["std"]

contrib/test.sh

@@ -58,7 +58,6 @@ then
     cargo run --example parse
     cargo run --example sign_multisig
     cargo run --example verify_tx > /dev/null
-    cargo run --example psbt
     cargo run --example xpub_descriptors
     cargo run --example taproot --features=compiler
     cargo run --example psbt_sign_finalize --features=base64