ref: delete unreachable upstream-fetcher modules

Stacked on the modifications PR. Now that no live code path references
the per-package fetchers, the shared HTTP/parsing helpers, the
in-process normalizer, or the example template, delete them. Pure
deletion — no behavior change.

- ~93 per-package <pkg>/releases.js fetcher modules.
- _common/{brew,fetcher,git-tag,gitea,github,github-source,
  githubish,githubish-source}.js shared HTTP/parsing helpers.
- _webi/normalize.js in-process normalization layer (cache files
  arrive normalized from webicached).
- _example/releases.js fetcher template for new packages.

The Go cache daemon (webicached) is now the sole producer of release
metadata; the Node process never makes an upstream request.

git/releases.js

@@ -1,33 +0,0 @@
-'use strict';
-
-var github = require('../_common/github.js');
-var owner = 'git-for-windows';
-var repo = 'git';
-
-module.exports = function () {
-  // TODO support mac and linux tarballs
-  return github(null, owner, repo).then(function (all) {
-    // See https://github.com/git-for-windows/git/wiki/MinGit
-    // also consider https://github.com/git-for-windows/git/wiki/Silent-or-Unattended-Installation
-    all.releases = all.releases
-      .filter(function (rel) {
-        rel.os = 'windows';
-        rel._version = rel.version.replace(/\.windows.1.*/, '');
-        rel._version = rel._version.replace(/\.windows(\.\d)/, '$1');
-        return (
-          /MinGit/i.test(rel.name || rel.download) &&
-          !/busybox/i.test(rel.name || rel.download)
-        );
-      })
-      .slice(0, 20);
-    all._names = ['MinGit', 'git'];
-    return all;
-  });
-};
-
-if (module === require.main) {
-  module.exports().then(function (all) {
-    all = require('../_webi/normalize.js')(all);
-    console.info(JSON.stringify(all, null, 2));
-  });
-}