security/libsodium: Revert "security/libsodium: Update to 1.0.19"

This reverts commit 0ff061cd7a64813e1088f962c3b8521823f72bb1.

Revert update until creating consumers list to bump. There are at least
72 explicit consumers and some more implicit consumers. Hold on to old
version until creating complete list of consumers.

Approved by: blanket (runtime fixes)