fix(info): remove `ToolchainInfo#env`

BREAKING CHANGE: `toolchain_info` removes `ToochainInfo#env`.

Allowing access to the original `env` attribute of the `toolchain_info` target can result in unexpected errors. `env` is usual subject to Make variable and expand location expansion. The expansion is done in the scope of the original rule. Re-using the environment results in errors with miscalculated paths, etc.

If it is required to capture the environment variables for a binary, it is much better to use a rule that bakes the environment variables into the execution of the binary. This can be done with launcher scripts that write out the environment variables for later use.