[Grbl_Esp32 PR#588] Remove trivial defines

Weeded out all trivial defines I could find in the code. Defines are trivial if they are unused, or:

– defined only once and
– not used in an #if, #ifdef or #ifndef and
– not redefined or a pin and
– doesn’t redefine a symbol more than once

SpindleType was converted to an enum class, since it’s also trivial.

Build-all succeeds. Manually changed & validated the code using the previous PR as a basis.