[test/Object] - Cleanup the Object\obj2yaml.test a bit.

This makes 2 changes:

1) Removes unwind-section.elf-x86-64 object and the corresponding test case,
because SHT_X86_64_UNWIND is already tested here:
https://github.com/llvm-mirror/llvm/blob/master/test/tools/obj2yaml/section-type.yaml

2) Removes/partially moves "No such file or directory" test, because we already have a similar test here:
https://github.com/llvm-mirror/llvm/blob/master/test/tools/obj2yaml/invalid_input_file.test

Differential revision: https://reviews.llvm.org/D65570

llvm-svn: 368044