Remove stale references to "handwired/ferris"

The code was moved to the "ferris" directory.

Fixes the following commands:
```
qmk compile ~/qmk_firmware/keyboards/ferris/keymaps/default/keymap.json
qmk compile ~/qmk_firmware/keyboards/ferris/keymaps/pierrec83/keymap.json
```

Addresses this issue:
https://github.com/pierrechevalier83/ferris/issues/5

keyboards/ferris/keymaps/default/keymap.json

@@ -1,7 +1,7 @@
 {    "version": 1,
     "notes": "My awesome keymap",
     "documentation": "\"This file is a QMK Configurator export. You can import this at <https://config.qmk.fm>. It can also be used directly with QMK's source code.\n\nTo setup your QMK environment check out the tutorial: <https://docs.qmk.fm/#/newbs>\n\nYou can convert this file to a keymap.c using this command: `qmk json2c {keymap}`\n\nYou can compile this keymap using this command: `qmk compile {keymap}`\"\n",
-    "keyboard": "handwired/ferris",
+    "keyboard": "ferris/0_1",
     "keymap": "default",
     "layout": "LAYOUT",
     "layers": [