Fix flaky npm 6 peer dependency test

It looks like this spec has become flaky recently, not clear why but
seems to have fixed it by making the expectation compare the dependency
hash instead of the instance.

Also removed the alias on `npm6` as we no longer install npm7 as a npm package.

npm_and_yarn/helpers/lib/npm6/peer-dependency-checker.js

@@ -10,8 +10,8 @@
  *  - successful completion, or an error if there are peer dependency warnings
  */
 
-const npm = require("npm6");
-const installer = require("npm6/lib/install");
+const npm = require("npm");
+const installer = require("npm/lib/install");
 const { muteStderr, runAsync } = require("./helpers.js");
 
 function installArgsWithVersion(depName, desiredVersion, reqs) {

npm_and_yarn/helpers/lib/npm6/subdependency-updater.js

@@ -1,7 +1,7 @@
 const fs = require("fs");
 const path = require("path");
-const npm = require("npm6");
-const installer = require("npm6/lib/install");
+const npm = require("npm");
+const installer = require("npm/lib/install");
 const detectIndent = require("detect-indent");
 const removeDependenciesFromLockfile = require("./remove-dependencies-from-lockfile");
 

npm_and_yarn/helpers/lib/npm6/updater.js

@@ -16,8 +16,8 @@
  */
 const fs = require("fs");
 const path = require("path");
-const npm = require("npm6");
-const installer = require("npm6/lib/install");
+const npm = require("npm");
+const installer = require("npm/lib/install");
 const detectIndent = require("detect-indent");
 const { muteStderr, runAsync } = require("./helpers.js");