fix: Remove BQ27220 battery current USB detection for X3 (#3809)

Fix X3 startup I²C errors by routing USB/charging detection through the
SDK’s `BatteryMonitor`, which initializes the bus before reading the
fuel gauge.

Removes duplicate raw Wire helpers and keeps GPIO20 reserved for I²C on
X3. Battery percentage calculation and the positive-current charging
rule remain unchanged

We already read **actual battery current** from the X3’s BQ27220 **fuel
gauge**. It’s separate from the charging circuit.

The fix keeps the same reading: register `0x0C`, interpreted as signed
milliamps. It just routes that read through the SDK so I²C is
initialized first.

The distinction is **battery current versus USB connection**:

- Positive current → battery charging. - Negative current → battery
discharging. - Near zero → little battery current; USB could be
connected or disconnected.

So the current reading but we can't reliably infer from it is whether a
cable is attached especially when the battery is full. The UI currently
calls this “USB connected,” but the X3 implementation actually means
“battery current is positive."