opr: removed the unused static_inline initnode

This was included in the initial rbtree import, but is not used.

clang from OS X's Xcode 5.1 now warns about this unused function,
which is an error with --enable-checking .

Change-Id: I896504e83be317394418a7cc1b3f518e675fbb5b
Reviewed-on: http://gerrit.openafs.org/10887
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>