Remove mentions of removed `offset_to` method from `align_offset` docs
The `offset_to` method was deleted in https://github.com/rust-lang/rust/pull/52814.
The replacement for the removed method is `wrapping_offset_from`. However, neither method takes an `usize` as argument, so I don't think that it makes sense to mention them.
The errors are either:
- The meta-variable used in the right-hand side is not bound (or defined) in the
left-hand side.
- The meta-variable used in the right-hand side does not repeat with the same
kleene operator as its binder in the left-hand side. Either it does not repeat
enough, or it uses a different operator somewhere.
This change should have no semantic impact.
Also removes stage1, stage2 cfgs being passed to rustc to ensure that
stage1 and stage2 are only differentiated as a group (i.e., only through
not bootstrap).
