x11/xsel-conrad: minor fixes

• Plug memory leak [1]
• Convert to USES=localbase
• Drop unused X11 dependencies
• Unsilence install commands
• Convert DOCS to target helpers
• Reorder some lines

PR: 212261
Submitted by: Tobias Kortkamp <t@tobik.me>
Obtained from: OpenBSD Ports [1]
Approved by: maintainer timeout (2 months)
MFH: 2016Q4