src/stacktrace.c: remove in favour of stackprof

src/stacktrace.c: remove in favour of stackprof

Now that stackprof is added, the existing src/stacktrace.c tool is
officially obsolete as a demo -- it relies on a custom patchset for
Sysprof (communicating via pipe, not contributed to mainline, in
favour of the sysprof-live-unwinder tool which links elfutils as a
library), whereas stackprof pulls data from perf_events directly.

Likewise, stackprof includes all of the eu-stacktrace functionality
for logging/statistics.

* configure.ac: Remove eu-stacktrace related bits.
  The configure checks for stackprof are simpler (just perf_events.h
  and libpfm).
* config/elfutils.spec.in: Remove eu-stacktrace.
* po/POTFILES.in: Remove stacktrace.c.
* src/Makefile.am: Remove eu-stacktrace related bits.
* src/stacktrace.c: Remove.

Co-authored-by: <fche@redhat.com>
Signed-off-by: <serhei@serhei.io>