Delete our custom add_workspace_toml_entry logic in `create` subcommand

[pksunkara]

MSRV needed 1.75.0

rust-lang/cargo#12779

[filleduchaos]

Yeah this breaks cargo ws create - the package creation itself succeeds, but because the output from Cargo does not contain "Created" cargo workspaces assumes it failed

Std output of cargo new in a workspace (on nightly 2024-03-02):

    Creating library `foo` package
      Adding `foo` as member of workspace at `/some/path/to/workspace`

[sushruth]

I opened a PR for it potentially fixing this - #152