Remove Cygwin-oriented instructions (for installing HBase in Windows OS) from official reference materials

Cygwin-oriented instructions in the official reference materials (for installing HBase in a Windows environment) seem to be out of date and incorrect; a number of unresolved/unresolvable requests for help have been posted to dev@hbase.org and user@hbase.org mailing lists.

Discussions on dev@apache.org and HBase Slack channel resulted in (1) no volunteers to update/maintain the Cygwin-oriented instructions, and (2) several "+" votes and no "-" votes on the suggestion of removing Cygwin-oriented instructions from the official reference materials.

FUTURE POSSIBLE FOLLOW-UP: For the sake of setting up a development/testing/sandbox environment in Windows, it might be helpful to recommend the installation of a virtual machine environment (e.g. VirtualBox) in a Windows OS, followed by the installation of an appropriate flavor of Linux (e.g., Ubuntu) in the VM. After this, all the standard HBase installation/config/usage instructions can be followed.