Tracker v1.1 - fix pin 3 description in variant.h

[jonagnew]

Schematic shows the following:
Pin 3 is Vext on v1.1 - HIGH enables LDO for Vext rail which goes to:
GPS UC6580: GPS V_DET(8), VDD_IO(7), DCDC_IN(21), pulls up RESETN(17), D_SEL(33) and BOOT_MODE(34) through 10kR
GPS LNA SW7125DE: VCC(4), pulls up SHDN(5) through 10kR OLED: VDD, LEDA (through diode)

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