[Common] JGroups SYM_ENCRYPT requires unnecessary variable

In order to configure JGroups encryption using symmetric protocol user has to provide file and 5 env variables:

• JGROUPS_ENCRYPT_SECRET
• JGROUPS_ENCRYPT_NAME
• JGROUPS_ENCRYPT_PASSWORD
• JGROUPS_ENCRYPT_KEYSTORE_DIR
• JGROUPS_ENCRYPT_KEYSTORE

First of them, however has only usage in templates to correctly mount secret to the image.

Yet the scripts checks for its presence even they don't read from it anywhere. This issue is proposal to remove JGROUPS_ENCRYPT_SECRET from image scripts as it doesn't has any practical usage and only forces users that don't use templates to define any value if they want to use SYM_ENCRYPT. Other four env variables are enough to decide whether to configure feature or not.

Env shouldn't be also passed to the container through templates.