[compiler-rt] Remove unused formal parameters from allocateOneNode. NFC.

Summary: This is just a minor cleanup to the allocateOneNode interface.  The formals are no-longer used, so I just removed them.

Reviewers: davidxl, void

Reviewed By: davidxl

Subscribers: dberris, llvm-commits

Differential Revision: https://reviews.llvm.org/D52509

llvm-svn: 344073