Get-DbaHelpIndex - Fix SQL injection and remove SQL 2005 code path

- Escape single quotes in ObjectName to prevent SQL injection when
  building the @TableName DECLARE/SET statement
- Remove unused $SizesQuery2005 block and its conditional branching;
  Connect-DbaInstance -MinimumVersion 10 already enforces SQL 2008+
- Update docs to reflect SQL Server 2008+ minimum version requirement

(do Get-DbaHelpIndex)

Co-authored-by: Andreas Jordan <andreasjordan@users.noreply.github.com>

Author: github-actions[bot]