Fix `collections::VecMap`'s `PartialEq` implementation

Previously it took capacity into account.

Additionally remove the `ne` implementation of `RingBuf` which is the default
one anyway.
Merge pull request #20155 from tbu-/pr_vecmap_fiximpls

Fix `collections::VecMap`'s `PartialEq` implementation

Reviewed-by: Gankro