[SRU][Unstable/Q/P/N/J][PATCH 0/5] sources list generation using dwarfdump takes up to 0.5hr in build process (LP: #2104911)

[Juerg Haefliger]

BugLink: https://bugs.launchpad.net/bugs/2104911

[ Impact ]

In debian/rules.d/2-binary-arch.mk, stamp-build-% targets, we have:
```
# Collect the list of kernel source files used for this build. Need to do this
early
# before modules are stripped. Fail if the resulting file is empty.
find $(build_dir) \( -name vmlinux -o -name \*.ko \) -exec dwarfdump -i {} \; |
\
        grep -E 'DW_AT_(call|decl)_file' | sed -n 's|.*\s/|/|p' | sort -u > \
        $(build_dir)/sources.list
test -s $(build_dir)/sources.list
```

The process is single threaded and may takes up to half an hour to complete:
```
$ time ...

real 28m15.167s
user 54m32.917s
sys 4m32.531s
```

[ Fix ]

This takes way too long. Parallelization introduces new/different issues. Remove
the logic to collect the list of kernel source files during the build. We have
all the data in the debug packages and can extract it after the build.

This reverts the changes for bug 2086606.

[ Test Plan ]

Inspect the build logs and the content of the linux-buildinfo packages to verify
the data is no longer collected.

[ Where Problems Could Occur ]

Potential build failures.