Update comment and default exclude
Update comment and default exclude

- comments about (3)DES were inconsistent (one saying "keep 3DES" and
the other "exclude it")
- we don't have any DES or 3DES ciphersuite anyway, so no need to
exclude them or comment about it
- while at it, fix comment about ARIA: it's in the default config now

Signed-off-by: Manuel Pégourié-Gonnard <4ba0d615aeeda88e422ca8fba28fe2938485facf@arm.com>

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