[llvm-readelf][test] - Refine the sections-ext.test

[llvm-readelf][test] - Refine the sections-ext.test

The `sections-ext.test` is a test for ELF that is used
to test `--st`, `--sr` and `--sd` extension options for `-S`.

There are 2 problems with it:
1) It is broken, because for CHECK lines it contains there is
no corresponding `FileCheck` call.

2) It uses the precompiled object: `trivial.obj.elf-i386`.
This is the last ELF test where `trivial.obj.elf-i386` is used so we can get
rid of the binary and use an YAML description.

Also, there is a `Inputs/trivial.ll` file that describes how `trivial*` objects
in `Inputs` folders are created. I've removed it from `ELF`, because it is not
actual anymore (we have no more input binaries created with the use of trivial.ll there)
and copied the refined versions of it to `COFF`, `MachO` and `wasm` Input folders.

Differential revision: https://reviews.llvm.org/D86462