remove erroneous z2 define from pins_BTT_MANTA_M8P_V2_0

[ellensp]

Description

pins_BTT_MANTA_M8P_V2_0.h is a bit broken

It has a #define Z2_SERIAL_TX_PIN PB5 so Z2_SERIAL_TX_PIN is always on Motor4
But there are no other Z2 pins. So Z2 moves to first available unused E

This also breaks driver uarts for E0,E1 E2 and E3

This is what is defined

  #define X_SERIAL_TX_PIN                   PC13      // M1
  #define Y_SERIAL_TX_PIN                   PE3       // M2
  #define Z_SERIAL_TX_PIN                   PB9       // M3
  #define Z2_SERIAL_TX_PIN                  PB5       // M4
  #define E0_SERIAL_TX_PIN                  PG14      // M5
  #define E1_SERIAL_TX_PIN                  PG10      // M6
  #define E2_SERIAL_TX_PIN                  PD5       // M7
  #define E3_SERIAL_TX_PIN                  PC6       // M8

But this is what is needed

  #define X_SERIAL_TX_PIN                   PC13      // M1
  #define Y_SERIAL_TX_PIN                   PE3       // M2
  #define Z_SERIAL_TX_PIN                   PB9       // M3
  #define E0_SERIAL_TX_PIN                  PB5       // M4
  #define E1_SERIAL_TX_PIN                  PG14      // M5
  #define E2_SERIAL_TX_PIN                  PG10      // M6
  #define E3_SERIAL_TX_PIN                  PD5       // M7
  #define E4_SERIAL_TX_PIN                  PC6       // M8

Requirements

BTT_MANTA_M8P_V2_0 using stepper driver with UART

Benefits

Correct UART is used

Related Issues

Z2 stepper motor is only in sync with Z stepper motor when using 16 microsteps #27746