doc: crypto: Removing reference to use custom configs for Mbed TLS

-We don't support providing a pre-written Mbed TLS config file
 while building nrf_security. The Kconfig's used for configurations
 are parsed and handled in CMake logic and there is no standard way
 to extract information from a pre-written header-file and have that
 lead to changed CMake logic.

Signed-off-by: Frank Audun Kvamtrø <[email protected]>

Author: frkv

doc/nrf/libraries/security/nrf_security/doc/configuration.rst

@@ -32,9 +32,6 @@ Custom Mbed TLS configuration files
 
 The nRF Security Kconfig options are used to generate an Mbed TLS configuration file.
 
-Although not recommended, it is possible to provide a custom Mbed TLS configuration file by disabling :kconfig:option:`CONFIG_GENERATE_MBEDTLS_CFG_FILE`.
-See :ref:`nrf_security_tls_header`.
-
 Building with TF-M
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