Remove XFAIL flag from sanitize-coverage-old-pm.c

This test has started passing consistently on 32bit arm where underlying
core is reported as Armv7 or Thumbv7.
However it still fails intermittently on 32bit AArch32 reported as Armv8l.

https://lab.llvm.org/buildbot/#/builders/190/builds/20
https://lab.llvm.org/buildbot/#/builders/170/builds/41