Do no create sam.ldb in Samba C code.

The errors given when starting BIND9 on a non-existent sam.ldb are quite confusing. This gives a better 'no such file or directory'.

This matches what we do in python and ldb tools.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14579

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• (optional) This MR is just one part towards a larger feature.
• (optional, if backport required) Bugzilla bug filed and BUG: tag added
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code