Rollup merge of #53979 - alexcrichton:remove-repr-transparent-atomics-master, r=sfackler

Remove `#[repr(transparent)]` from atomics

Added in #52149 the discussion in #53514 is showing how we may not want to
actually add this attribute to the atomic types. While we continue to
debate #53514 this commit reverts the addition of the `transparent` attribute.
This should be a more conservative route which leaves us the ability to tweak
this in the future but in the meantime allows us to continue discussion as well.