xdebug-not-done -> xdebug

Summary: This changes the `XDEBUG_NAME` macro from `xdebug-not-done` to `xdebug` and also xdebug ini settings from `hhvm.xdebug-not-done.*` to  `xdebug.*`, matching php5 xdebug. This just involved a find and replace and updating `xdebug.enable` to use ini instead of hdf.

Closes a TODO in #3704.
Closes https://github.com/facebook/hhvm/pull/3779

Reviewed By: @ptarjan

Differential Revision: D1563675

Pulled By: @paulbiss