Revert "plugins/rust: restrict predicates-{tree,core} to {1.0.7,1.0.5}"
This reverts commit da7458d7.
The changes in MR #26 address the problem in a different way. After that PR, all CI pipelines using rustc < 1.64.0 will lock all packages, not just predicates, to the versions specified in Cargo.lock.msrv, while allowing CI pipelines with newer toolchains to use the latest version of predicates.