Use dedicated Tracker V2 sensor I2C pins

[csrutil]

Summary

• Move Tracker V2 sensor I2C pins out of the base board environment.
• Configure the Tracker V2 sensor environment to use ENV_PIN_SDA=17 and ENV_PIN_SCL=18.

Rationale

• Heltec's Tracker V2.3 pinmap shows GPIO17 and GPIO18 as exposed header GPIOs without onboard assignments to TFT, GNSS, LoRa FEM control, Vext control, ADC control, battery sense, USB, boot, or reset.
• Avoid GPIO3/GPIO4/GPIO5/GPIO7 because they are assigned to Vext_Ctrl, PA_CSD, PA_CTX, and VFEM_Ctrl.
• Avoid GPIO21 and GPIO38-GPIO42 because they are used by the TFT.
• Avoid GPIO33-GPIO35 because they are used by GNSS.
• Avoid GPIO19/GPIO20 because they are used by USB.
• ESP32-S3 supports routing I2C to suitable GPIOs, so GPIO17/GPIO18 are a clean dedicated sensor I2C pair for this environment.

Reference pinmap: https://heltec.org/wp-content/uploads/2025/09/Tracker_v2.3pinmap.png