rustc: Remove special treatment for Freeze and NoFreeze

Fixes #12577
arena: Remove Freeze / NoFreeze
sync: Remove Freeze / NoFreeze
std::comm: Remove Freeze / NoFreeze
cell: Remove Freeze / NoFreeze
std: Remove the Freeze kind and the NoFreeze marker
test: Remove Freeze / NoFreeze from tests
doc: Remove Freeze / NoFreeze from docs
auto merge of #13076 : FlaPer87/rust/remove-freeze, r=alexcrichton

This PR removes the `Freeze` kind and the `NoFreeze` marker completely.

Fixes #12577

cc @nikomatsakis r?