textproc/raptor2: Clean up port and backport upstream commit

• Backport upstream commit 4dbc4c1da2a033c497d84a1291c46f416a9cac51 to fix build with newer versions of libxml2
• Use USES= localbase and remove unnecessary CONFIGURE_ARGS
• Move USE_LDCONFIG

PR: 273116
Approved by: kde (jhale)
Sponsored by: Blinkinblox