[msan] Remove a failing test from MemorySanitizer.ICmpRelational

This is a follow-up to r302787, which broke MemorySanitizer.ICmpRelational.

MSan is now reporting a false positive on the following test case:
  TestForNotPoisoned((poisoned(-1, 0x80000000U) >= poisoned(-1, 0U)))
, which is sort of anticipated, because we're approximating the comparison
with an OR of the arguments' shadow values.

llvm-svn: 302887