removed openzeppelin dependency

.gitignore

@@ -1,3 +1,4 @@
 node_modules
+build
 temp
 keys.json

contracts/ERC165/ERC165Removable.sol

@@ -1,20 +1,61 @@
 // SPDX-License-Identifier: MIT;
-pragma solidity ^0.6.0;
+pragma solidity 0.6.2;
 
-import "@openzeppelin/contracts/introspection/ERC165.sol";
+import "./IERC165.sol";
 
 /**
  * @dev Custom implementation of the IERC165 interface.
  * This is contract implemented by OpenZeppelin but extended with
  * _removeInterface function
  */
-contract ERC165Removable is ERC165 {
-    /**
-     * @dev Removes support of the interface
-     * @param interfaceId Interface Id
-     */
-    function _removeInterface(bytes4 interfaceId) internal {
-        require(_supportedInterfaces[interfaceId], "ERC165: unknown interface id");
-        _supportedInterfaces[interfaceId] = false;
-    }
+contract ERC165Removable is IERC165 {
+  /**
+    * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+    */
+  bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
+
+  /**
+    * @dev Mapping of interface ids to whether or not it's supported.
+    */
+  mapping(bytes4 => bool) private _supportedInterfaces;
+
+  constructor () internal {
+      // Derived contracts need only register support for their own interfaces,
+      // we register support for ERC165 itself here
+      _registerInterface(_INTERFACE_ID_ERC165);
+  }
+
+  /**
+    * @dev See {IERC165-supportsInterface}.
+    *
+    * Time complexity O(1), guaranteed to always use less than 30 000 gas.
+    */
+  function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
+      return _supportedInterfaces[interfaceId];
+  }
+
+  /**
+    * @dev Registers the contract as an implementer of the interface defined by
+    * `interfaceId`. Support of the actual ERC165 interface is automatic and
+    * registering its interface id is not required.
+    *
+    * See {IERC165-supportsInterface}.
+    *
+    * Requirements:
+    *
+    * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
+    */
+  function _registerInterface(bytes4 interfaceId) internal virtual {
+      require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
+      _supportedInterfaces[interfaceId] = true;
+  }
+
+  /**
+    * @dev Removes support of the interface
+    * @param interfaceId Interface Id
+    */
+  function _removeInterface(bytes4 interfaceId) internal {
+      require(_supportedInterfaces[interfaceId], "ERC165: unknown interface id");
+      _supportedInterfaces[interfaceId] = false;
+  }
 }

contracts/ERC165/IERC165.sol

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface of the ERC165 standard, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-165[EIP].
+ *
+ * Implementers can declare support of contract interfaces, which can then be
+ * queried by others ({ERC165Checker}).
+ *
+ * For an implementation, see {ERC165}.
+ */
+interface IERC165 {
+    /**
+     * @dev Returns true if this contract implements the interface defined by
+     * `interfaceId`. See the corresponding
+     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
+     * to learn more about how these ids are created.
+     *
+     * This function call must use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool);
+}