Remove misleading documentation on Java support in core-tools

[satvu]

This document is misleading. Java is not supported in core-tools (see here and see supported local development environments). While a core-tools installation is necessary for these environments, it should not be used directly.

Additionally, instructions in this doc such as func new --template "Http Trigger" --name MyHttpTrigger are not supported and will result in errors.

This issue tracks the removal of the misleading doc.