Tests: strip ELF symbols from debuginfo-data executables with separate DWARF

Stripping the symbols prevents the framework from falling back to ELF
lookup should the separate DWARF files be missing, which would cause
tests to succeed when they should fail.

Signed-off-by: Antoine Busque <abusque@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>