Fix broken xrefs (#2153)

* fix mentions of drafts.adoc

* fix 721.adoc

docs/modules/ROOT/pages/releases-stability.adoc

@@ -28,7 +28,7 @@ Every several months a new major release may come out. These are not scheduled,
 
 On the https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v2.0.0[OpenZeppelin 2.0 release], we committed ourselves to keeping a stable API. We aim to more precisely define what we understand by _stable_ and _API_ here, so users of the library can understand these guarantees and be confident their project won't break unexpectedly.
 
-In a nutshell, the API being stable means _if your project is working today, it will continue to do so_. New contracts and features will be added in minor releases, but only in a backwards compatible way. The exception to this rule are contracts in the xref:api:drafts.adoc[Drafts] category, which should be considered unstable.
+In a nutshell, the API being stable means _if your project is working today, it will continue to do so_. New contracts and features will be added in minor releases, but only in a backwards compatible way.
 
 [[versioning-scheme]]
 === Versioning Scheme

docs/modules/ROOT/pages/utilities.adoc

@@ -97,4 +97,4 @@ If you need support for more powerful collections than Solidity's native arrays
 
 Want to check if an address is a contract? Use xref:api:utils.adoc#Address[`Address`] and xref:api:utils.adoc#Address-isContract-address-[`Address.isContract()`].
 
-Want to keep track of some numbers that increment by 1 every time you want another one? Check out xref:api:drafts.adoc#Counter[`Counter`]. This is useful for lots of things, like creating incremental identifiers, as shown on the xref:721.adoc[ERC721 guide].
+Want to keep track of some numbers that increment by 1 every time you want another one? Check out xref:api:utils.adoc#Counters[`Counters`]. This is useful for lots of things, like creating incremental identifiers, as shown on the xref:erc721.adoc[ERC721 guide].