Move recent/minimal lock files

A while back we added two lock files that were to track dependencies of
two successful test runs, one with a minimal set of dependencies and one
with a recent set of dependencies (ie, recent dependency versions). We
never used these lock files in CI however.

In preparation for using the lock files in CI, and in order to be
uniform with `rust-bitcoin`, move the lock files to the crate root and
rename them to:

- Cargo-minimal.lock
- Cargo-recent.lock

Author: tcharding