[sanitizer] Remove the definition of xdr_ops.

User-visible instances of xdr_ops always seem to be allocated statically, and
don't need unpoisoning. Also, it's size differs between platforms.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208851 91177308-0d34-0410-b5e6-96231b3b80d8