Remove add-performance-global.js

Node defines the `performance` global since version 16. Part of #25.

Note that this will require changes in m3api-query and m3api-oauth2,
which also import this file in their tests.

CHANGES.md

@@ -10,6 +10,8 @@ but this file may sometimes contain later improvements (e.g. typo fixes).
 - BREAKING CHANGE:
   m3api now requires at least Node.js version 16,
   up from Node 12.22.0 or Node 14.17.0 previously.
+  As part of this, `add-performance-global.js` has been removed,
+  as it is no longer needed.
 - Improved `README.md` formatting for npmjs.com.
 
 ## v0.7.3 (2023-04-11)

README.md

@@ -444,7 +444,7 @@ The stable, public interface comprises the following items:
 
 The internal interface additionally comprises the following items:
 
-- The paths / existence of the `axios.js`, `fetch.js`, `combine.js` and `add-performance-global.js` files.
+- The paths / existence of the `axios.js`, `fetch.js` and `combine.js` files.
 
 - All exports of those files, or of files in the public interface, that have not been marked `@private`.
 

node.js

@@ -1,6 +1,5 @@
 import { AxiosSession } from './axios.js';
 import { mixCombiningSessionInto } from './combine.js';
-import './add-performance-global.js';
 
 export default class NodeSession extends AxiosSession {
 }

test/unit/sessions.js

@@ -1,5 +1,4 @@
 import { Session } from '../../core.js';
-import '../../add-performance-global.js';
 import { expect } from 'chai';
 
 /**