This patch extends D58439 (`llvm/test/{yaml2obj,obj2yaml}/**/*.yaml`) and runs all
`llvm/test/**/*.yaml`
Many directories have configured `.yaml` (see the deleted lit.local.cfg
files). Yet still some don't configure .yaml and have caused stale tests:
* 8c5825befb test/llvm-readobj
* bdc3134e23 test/ExecutionEngine
Just hoist .yaml to `llvm/test/lit.cfg.py`. Also delete .cxx which is
not used. The number of tests running on my machine increases from 38304 to 38309.
The list of new tests:
```
ExecutionEngine/RuntimeDyld/X86/ELF_x86-64_none.yaml
Object/archive-error-tmp.txt
tools/llvm-ar/coff-weak.yaml
tools/llvm-readobj/ELF/verneed-flags.yaml
tools/obj2yaml/COFF/bss.s
```
Reviewed By: grimar, jhenderson, rupprecht
Differential Revision: https://reviews.llvm.org/D83350
