DebugInfo: Remove some unneeded conditionals now that DIBuilder no longer emits zero-length arrays as {i32 0}

A bunch of test cases needed to be cleaned up for this, many my fault -
when implementid imported modules I updated test cases by simply
duplicating the prior metadata field - which wasn't always the empty
metadata entry.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200731 91177308-0d34-0410-b5e6-96231b3b80d8