Remove alpha notice. (quantumlib#5811)

Fixes quantumlib#5761

.github/workflows/ci.yml

@@ -247,7 +247,7 @@ jobs:
     strategy:
       matrix:
         python-version: [ '3.7', '3.8', '3.9', '3.10' ]
-    runs-on: macos-10.15
+    runs-on: macos-12
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v1

README.rst

@@ -121,14 +121,4 @@ For a powerful quantum circuit simulator that integrates well with Cirq, we reco
 
 Finally, `ReCirq <https://github.com/quantumlib/ReCirq>`__ contains real world experiments using Cirq.
 
-
-Alpha Disclaimer
-----------------
-
-**Cirq is currently in alpha.**
-We may change or remove parts of Cirq's API when making new releases.
-To be informed of deprecations and breaking changes, subscribe to the
-`cirq-announce google group mailing list <https://groups.google.com/forum/#!forum/cirq-announce>`__.
-
-
 Cirq is not an official Google product. Copyright 2019 The Cirq Developers

docs/start/install.md

@@ -10,13 +10,6 @@ If you want to create a development environment, see the [development page](/cir
 
 ---
 
-## Alpha disclaimer
-
-**Cirq is currently in alpha.**
-We may change or remove parts of Cirq's API when making new releases.
-To be informed of deprecations and breaking changes, subscribe to the
-[cirq-announce google group mailing list](https://groups.google.com/forum/#!forum/cirq-announce).
-
 ## Python version supprt
 
 Cirq currently supports python 3.7 and later.

docs/start/intro.ipynb

@@ -140,9 +140,7 @@
     "id": "09zRgohCMiBs"
    },
    "source": [
-    "This cell should run successfully, and the output should in fact be the grid of qubits for the Sycamore device. If so, the install worked!\n",
-    "\n",
-    "> Be aware that Cirq is still alpha software, meaning **breaking changes can happen at any time**. If you don't want your project to suddenly go from working to not working when we a new version is released, you should depend on a *specific version* of Cirq and periodically bump that version to the latest one. For example, you can run `pip install cirq==x.y.z` to install version `x.y.z` of Cirq."
+    "This cell should run successfully, and the output should in fact be the grid of qubits for the Sycamore device. If so, the install worked!\n"
    ]
   },
   {

release.md

@@ -1,7 +1,6 @@
 # Versioning and Releases
 
-Cirq is currently (as of May 2020) alpha, and so has a MAJOR version
-of 0. Below is info on how we version releases, and how the releases
+Below is info on how we version releases, and how the releases
 themselves are created. Note that development is done on the `master`
 branch, so if you want to use a more stable version you should use one
 of the [releases](https://github.com/quantumlib/Cirq/releases) or