[2.0.x] Simplify bltouch configuration (#9488)

Marlin/src/inc/Conditionals_LCD.h

 
   #if ENABLED(Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN)
     #undef Z_MIN_ENDSTOP_INVERTING
-    #define Z_MIN_ENDSTOP_INVERTING false
+    #define Z_MIN_ENDSTOP_INVERTING Z_MIN_PROBE_ENDSTOP_INVERTING
     #define TEST_BLTOUCH() _TEST_BLTOUCH(Z_MIN)
   #else
     #define TEST_BLTOUCH() _TEST_BLTOUCH(Z_MIN_PROBE)