Re-use lightning-invoice crate exported by gl-client

[ok300]

This PR replaces our explicit lightning-invoice dependency with the gl-client one, similar to how #779 did the same for the bitcoin crate.

The benefits we get are:

• we reduce the dependency tree and binary size
  • no need to bundle both our lightning-invoice version and the one from gl-client
• we help our SDK users easily choose the right lightning-invoice version
  • they can simply access it with breez_sdk_core::lightning_invoice

[ok300]

As discussed with Roei, I removed the re-exports, as we don't use those crates in our public APIs.

[roeierez]

LGTM