ci: remove .cargo/audit.toml

All ignores are not applicable anymore:
- `gdbstub` - resolved upstream
  daniel5151/gdbstub#168
- `rand` - moved to deny.toml
- `anyhow` - is not directly used by our crates and `cargo-deny`
  correctly ignores it

Signed-off-by: Egor Lazarchuk <yegorlz@amazon.co.uk>

Author: ShadowCurse