Refactor helix/pico (#25428)

Refactor helix/pico

- Updates keyboard aliases accordingly
- Removes redundant back, base, sc, under, & qmk_conf revisions
- Migrates legacy defines and configuration to keyboard.json
- Tidy's keymap and migrates to JSON
- Fixes RGB configuration to illuminate 25 LEDs per half
- Enables standard features (bootmagic, extrakey, etc.)

data/mappings/keyboard_aliases.hjson

@@ -257,12 +257,6 @@
     "handwired/jscotto/scottostarter": {
         "target": "handwired/scottokeebs/scottostarter"
     },
-    "helix/pico/sc/back": {
-        "target": "helix/pico/sc"
-    },
-    "helix/pico/sc/under": {
-        "target": "helix/pico/sc"
-    },
     "helix/rev2/back/oled": {
         "target": "helix/rev2/back"
     },
@@ -2284,9 +2278,6 @@
     "handwired/dygma/raise": {
         "target": "handwired/dygma/raise/ansi"
     },
-    "helix/pico": {
-        "target": "helix/pico/base"
-    },
     "helix": {
         "target": "helix/rev2/base"
     },