nrf_security: disable CONFIG_MBEDTLS_SSL_CONTEXT_SERIALIZATION by default

It used to be enabled by default, and could result in check_config.h
errors from Mbed TLS due to missing prerequisites.
It doesn't seem to be serving any purpose so let's just stop enabling
it by default.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>

Author: tomi-font

subsys/nrf_security/Kconfig.tls

@@ -241,7 +241,6 @@ config MBEDTLS_SSL_ALL_ALERT_MESSAGES
 
 config MBEDTLS_SSL_CONTEXT_SERIALIZATION
 	bool "Serialization of TLS context structures"
-	default y
 	help
 	  This setting enables serialization of TLS structures, through use of
 	  the mbedtls_ssl_context_save() and mbedtls_ssl_context_load().