Remove outdated note about hooks from documentation (#3789)

Co-authored-by: Francisco <frangio.1@gmail.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

docs/modules/ROOT/pages/extending-contracts.adoc

@@ -103,13 +103,6 @@ contract ERC20WithSafeTransfer is ERC20 {
 
 Using hooks this way leads to cleaner and safer code, without having to rely on a deep understanding of the parent's internals.
 
-[NOTE]
-====
-Hooks are a new feature of OpenZeppelin Contracts v3.0.0, and we're eager to learn how you plan to use them!
-
-So far, the only available hook is `_beforeTransferHook`, in all of xref:api:token/ERC20.adoc#ERC20-_beforeTokenTransfer-address-address-uint256-[`ERC20`], xref:api:token/ERC721.adoc#ERC721-_beforeTokenTransfer-address-address-uint256-[`ERC721`], xref:api:token/ERC777.adoc#ERC777-_beforeTokenTransfer-address-address-address-uint256-[`ERC777`] and xref:api:token/ERC1155.adoc#ERC1155-_beforeTokenTransfer-address-address-address-uint256---uint256---bytes-[`ERC1155`]. If you have ideas for new hooks, let us know!
-====
-
 === Rules of Hooks
 
 There's a few guidelines you should follow when writing code that uses hooks in order to prevent issues. They are very simple, but do make sure you follow them: