rebased
corrected spelling
changed to #elif for error

Still with MIN_Z_HEIGHT_FOR_HOMING but con be done with (folder wide) search-replace when we have a better name.

update old comments
update or delete deprecated definitions
complement forgotten updates
adjust spacing
some cosmetic changes

As suggested by @max-pau in #3073 - #3074

files.

Redo of #2939 rebased against RCBugFix

Renamed `WARN_REDUCED_ACCURACY` to `DISABLE_REDUCED_ACCURACY_WARNING`

Changed the condition for blinking from
```
#if ENABLED(WARN_REDUCED_ACCURACY)
```
to
```
#if DISABLED(DISABLE_REDUCED_ACCURACY_WARNING)
```

This formalizes the dependency of MANUAL_BED_LEVELING on
MESH_BED_LEVELING

- Include aligned comment about new SDSUPPORT behavior

Instead of changing SDEXTRASLOW variable to a slower speed,  the new
SDULTRASLOW is used for rigidbot panel.

Instead of changing SDEXTRASLOW variable to a slower speed,  the new
SDULTRASLOW is used for rigidbot panel.

• Removing trailing whitespace
• Adjusting indention for better readability
• Removing duplicated entries

Analog to https://github.com/MarlinFirmware/MarlinDev/pull/250 by
@RicardoGA

Restore the Babystep Multiplicator functionality and now it's available
for X/Y/Z

Add SDEXTRASLOW which runs the SD card at SPI_QUARTER_SPEED. Quarter speed is needed for RIGIDBOT_PANEL