remove dependency on reverted const type id

[KodrAus]

We were going to depend on const_type_id, but that feature was reverted before it was stabilized.

I'm working on a refactoring that changes this, but in the meantime anybody depending on kv_unstable and building on 1.47.0 is broken. This just removes the expectation that 1.47.0 will allow const_type_id.

[Karrq]

Is this perhaps the expected error to find on 1.47?
I'm currently trying to investigate who enables the kv feature in my workspace

error[E0635]: unknown feature `const_type_id`
 --> /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/value-bag-1.0.0-alpha.5/src/lib.rs:3:54
  |
3 | #![cfg_attr(value_bag_capture_const_type_id, feature(const_type_id))]
  |                                                      ^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0635`.
error: could not compile `value-bag`.