boards: Remove nRF54LM20A PDK and its references

Removing wrongly named devkit and change/remove all its references.

Signed-off-by: Karol Lasończyk <[email protected]>

Author: kl-cruz

.github/test-spec.yml

@@ -592,7 +592,7 @@
 
 "CI-test-low-level":
   - "applications/hpf/**/*"
-  - "boards/nordic/nrf54lm20apdk/**/*"
+  - "boards/nordic/nrf54lm20pdk/**/*"
   - "boards/nordic/nrf54lv10apdk/**/*"
   - "drivers/gpio/**/*"
   - "dts/bindings/gpio/**/*"