remove appsxcale (unmaintained since 2020)

- ref. AppScale/gts#3230
- https://github.com/AppScale/gts/commits/master
- ref. #405

README.md

@@ -169,7 +169,6 @@ _See also: [IT Asset Management](#it-asset-management)_
 
 **[`^        back to top        ^`](#awesome-sysadmin)**
 
-- [AppScale](https://github.com/AppScale/appscale) - Cloud software with Google App Engine compatibility.
 - [Archipel](http://archipelproject.org/) - Manage and supervise virtual machines using Libvirt.
 - [CloudStack](http://cloudstack.apache.org/) - Cloud computing software for creating, managing, and deploying infrastructure cloud services.
 - [Cobbler](http://cobbler.github.io/) - Cobbler is a Linux installation server that allows for rapid setup of network installation environments.