Remove redundant check for slot->allocated
Remove redundant check for slot->allocated

This check became redundant when support for direct access to key
slots was removed.

ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls