Disable unneeded plugins in StrongSwan

[dguido]

We definitely don't need to load all of this code.

00[LIB] loaded plugins: charon test-vectors aes rc2 sha1 sha2 md4 md5 random nonce x509 revocation constraints pubkey pkcs1 pkcs7 pkcs8 pkcs12 pgp dnskey sshkey pem openssl fips-prf gmp agent xcbc hmac gcm attr kernel-netlink resolve socket-default connmark stroke updown

[jackivanov]

I left these plugins:

strongswan_enabled_plugins:
  - aes
  - gcm
  - hmac
  - kernel-netlink
  - nonce
  - openssl
  - pem
  - pgp
  - pkcs12
  - pkcs7
  - pkcs8
  - pubkey
  - random
  - revocation
  - sha2
  - socket-default
  - stroke
  - x509