samples: crypto: psa_tls: Remove references to nrf54lm20pdk

Target nrf54lm20pdk was renamed to nrf54lm20dk.
Remove obsolete target from README file.

Signed-off-by: Sebastian Głąb <[email protected]>

Author: nordic-segl

samples/crypto/psa_tls/README.rst

@@ -110,7 +110,6 @@ The table mirrors the test setup used for TLS verification.
            - RSA not supported
            - Also supports :ref:`PSA Crypto nrf_oberon driver<nrf_security_drivers_oberon>`
          * - ``nrf54lm20dk/nrf54lm20a/cpuapp``
-             ``nrf54lm20pdk/nrf54lm20/cpuapp``
            - :ref:`PSA Crypto CRACEN driver<nrf_security_drivers_cracen>`
            - No
            - Yes
@@ -149,7 +148,6 @@ The table mirrors the test setup used for TLS verification.
            - RSA not supported
            - Also supports :ref:`PSA Crypto nrf_oberon driver<nrf_security_drivers_oberon>`
          * - ``nrf54lm20dk/nrf54lm20a/cpuapp``
-             ``nrf54lm20pdk/nrf54lm20/cpuapp``
            - :ref:`PSA Crypto CRACEN driver<nrf_security_drivers_cracen>`
            - No
            - Yes