Remove ERC721ASetOwnersExplicit extension

contracts/mocks/ERC721AMock.sol

@@ -73,7 +73,11 @@ contract ERC721AMock is ERC721A {
         return _ownershipAt(index);
     }
 
-    function getOwnershipOf(uint index) public view returns (TokenOwnership memory) {
+    function getOwnershipOf(uint256 index) public view returns (TokenOwnership memory) {
         return _ownershipOf(index);
     }
+
+    function initializeOwnershipAt(uint256 tokenId) public {
+        _initializeOwnershipAt(tokenId);
+    }
 }

test/ERC721A.test.js

@@ -454,6 +454,21 @@ const createTestSuite = ({ contract, constructorArgs }) =>
             expect(await this.erc721a.exists(this.tokenIdToBurn)).to.be.false;
           });
         });
+
+        describe('_initializeOwnershipAt', async function () {
+          it('successfuly sets ownership of empty slot', async function () {
+            const lastTokenId = this.addr3.expected.tokens[2];
+            expect(await this.erc721a.ownerOf(lastTokenId)).to.be.equal(this.addr3.address);
+            const tx1 = await this.erc721a.initializeOwnershipAt(lastTokenId);
+            expect(await this.erc721a.ownerOf(lastTokenId)).to.be.equal(this.addr3.address);
+            const tx2 = await this.erc721a.initializeOwnershipAt(lastTokenId);
+
+            // We assume the initialization worked due to less gas used by the 2nd txn
+            const receipt1 = await tx1.wait();
+            const receipt2 = await tx2.wait();
+            expect(receipt1.gasUsed.toNumber()).to.be.greaterThan(receipt2.gasUsed.toNumber());
+          });
+        });
       });
 
       context('test mint functionality', function () {

test/extensions/ERC721AQueryable.test.js

@@ -311,12 +311,3 @@ describe(
     constructorArgs: ['Azuki', 'AZUKI', 1],
   })
 );
-
-describe(
-  'ERC721AQueryableOwnersExplicit',
-  createTestSuite({
-    contract: 'ERC721AQueryableOwnersExplicitMock',
-    constructorArgs: ['Azuki', 'AZUKI'],
-    initializeOwnersExplicit: true,
-  })
-);