Revert "feat(github): long-term datasource caching (#15653)"

This reverts commit 2e957ba.

lib/modules/datasource/github-releases/__snapshots__/index.spec.ts.snap

@@ -0,0 +1,64 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`modules/datasource/github-releases/index getReleases returns releases 1`] = `
+Object {
+  "registryUrl": "https://github.com",
+  "releases": Array [
+    Object {
+      "gitRef": "1.0.0",
+      "releaseTimestamp": "2020-03-09T11:00:00.000Z",
+      "version": "1.0.0",
+    },
+    Object {
+      "gitRef": "v1.1.0",
+      "releaseTimestamp": "2020-03-09T10:00:00.000Z",
+      "version": "v1.1.0",
+    },
+    Object {
+      "gitRef": "2.0.0",
+      "isStable": false,
+      "releaseTimestamp": "2020-04-09T10:00:00.000Z",
+      "version": "2.0.0",
+    },
+  ],
+  "sourceUrl": "https://github.com/some/dep",
+}
+`;
+
+exports[`modules/datasource/github-releases/index getReleases supports ghe 1`] = `
+Object {
+  "releases": Array [
+    Object {
+      "gitRef": "a",
+      "isStable": undefined,
+      "releaseTimestamp": "2020-03-09T13:00:00Z",
+      "version": "a",
+    },
+    Object {
+      "gitRef": "v",
+      "isStable": undefined,
+      "releaseTimestamp": "2020-03-09T12:00:00Z",
+      "version": "v",
+    },
+    Object {
+      "gitRef": "1.0.0",
+      "isStable": undefined,
+      "releaseTimestamp": "2020-03-09T11:00:00Z",
+      "version": "1.0.0",
+    },
+    Object {
+      "gitRef": "v1.1.0",
+      "isStable": undefined,
+      "releaseTimestamp": "2020-03-09T10:00:00Z",
+      "version": "v1.1.0",
+    },
+    Object {
+      "gitRef": "2.0.0",
+      "isStable": false,
+      "releaseTimestamp": "2020-04-09T10:00:00Z",
+      "version": "2.0.0",
+    },
+  ],
+  "sourceUrl": "https://git.enterprise.com/some/dep",
+}
+`;