* GH-8732 Don't remove JDBC message if other groups
Fixes https://github.com/spring-projects/spring-integration/issues/8732
When same message is added into different groups,
its record in the `INT_MESSAGE` must remain until the last group is removed
* Improve `JdbcMessageStore.DELETE_MESSAGES_FROM_GROUP` SQL
to ignore those messages for removal which has other group records in the `INT_GROUP_TO_MESSAGE` table
**Cherry-pick to `6.1.x`, `6.0.x` & `5.5.x`**
* * Fix `JdbcMessageStore.removeMessage()` and `removeMessagesFromGroup()`
to remove from `INT_MESSAGE` only if there is no other records in `INT_GROUP_TO_MESSAGE`
* * Improve `MessageStore.removeMessage()` Javadoc
mentioning `MessageGroupStore` specifics
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