NONOS SDK clean-up (#8770)

Remove nonos-sdk-v2.2.0-28-g89920dc aka 3v0, since we have a real v3
Remove 3.0.0...3.0.4 to reduce overhead in maintaining a bunch or binary patches
Update our docs and menu opts to mention 'experimental' status

Old versions still remains in git history, so anyone wanting to play around with 3.0.x could still make use of that work

doc/esp8266wifi/client-class.rst

@@ -49,6 +49,7 @@ This API frees up resources used by the connection. Consider using it instead of
 *Example:*
 
 .. code:: cpp
+
    # define MIN_HEAP_FREE 20000 // or whatever min available heap memory convienent for your application 
    auto client = server.accept();
    // ... do something with the client object ...

doc/esp8266wifi/generic-class.rst

@@ -227,7 +227,11 @@ Other Function Calls
     bool  enableAP (bool enable)
     int  hostByName (const char *aHostname, IPAddress &aResult)
 
-    appeared with SDK pre-V3:
+
+Also, when using NONOS SDK v3:
+
+.. code:: cpp
+
     uint8_t getListenInterval ();
     bool isSleepLevelMax ();
 

doc/ideoptions.rst

@@ -219,13 +219,25 @@ Erase Flash
 
 -  ``All Flash``: WiFi settings and Filesystems are erased.
 
-Espressif Firmware
+NONOS SDK Version
 ~~~~~~~~~~~~~~~~~~
 
-There are a number of available espressif firmwares.  The first / default
-choice is fine.  Only try with others after reading on the issue tracker
-that something has to be tried with them.  Note that Espressif obsoleted
-all of them at the time of writing.
+Our Core is based on [Espressif NONOS SDK](https://github.com/espressif/ESP8266_NONOS_SDK).
+
+- **2.2.1+100 (190703)** (default)
+- 2.2.1+119 (191122)
+- 2.2.1+113 (191105)
+- 2.2.1+111 (191024)
+- 2.2.1+61 (190313)
+- 2.2.1 (legacy)
+- 3.0.5 (experimental)
+
+See our issue tracker in regards to default version selection.
+
+* `#6724 (comment) <https://github.com/esp8266/Arduino/pull/6724#issuecomment-556243781>`__
+* `#6826 <https://github.com/esp8266/Arduino/pull/6826>`__
+
+Notice that 3.x.x is provided **as-is** and remains **experimental**.
 
 SSL Support
 ~~~~~~~~~~~