@0x/contracts-zero-ex: Remove UniswapFeature

`@0x/contracts-zero-ex`: Fix broken tests.

contracts/zero-ex/test/features/meta_transactions_test.ts

@@ -301,7 +301,7 @@ blockchainTests.resets('MetaTransactions feature', env => {
                 new ZeroExRevertErrors.MetaTransactions.MetaTransactionCallFailedError(
                     mtxHash,
                     actualCallData,
-                    new StringRevertError('FAIL').toString(),
+                    new StringRevertError('FAIL').encode(),
                 ),
             );
         });
@@ -469,7 +469,7 @@ blockchainTests.resets('MetaTransactions feature', env => {
                         mtxHash,
                         signers[0],
                         signature,
-                    ).toString(),
+                    ).encode(),
                 ),
             );
         });

contracts/zero-ex/test/features/ownable_test.ts

@@ -102,7 +102,7 @@ blockchainTests.resets('Ownable feature', env => {
             return expect(tx).to.revertWith(
                 new ZeroExRevertErrors.Ownable.MigrateCallFailedError(
                     testMigrator.address,
-                    new StringRevertError('OOPSIE').toString(),
+                    new StringRevertError('OOPSIE').encode(),
                 ),
             );
         });

contracts/zero-ex/test/features/token_spender_test.ts

@@ -98,7 +98,7 @@ blockchainTests.resets('TokenSpender feature', env => {
                 tokenFrom,
                 tokenTo,
                 tokenAmount,
-                new StringRevertError('TestTokenSpenderERC20Token/Revert').toString(),
+                new StringRevertError('TestTokenSpenderERC20Token/Revert').encode(),
             );
             return expect(tx).to.revertWith(expectedError);
         });