Fix: Remove test_seek_empty_packet and test_seek_big_trace from SCRIPT_LIST

Fix: Remove test_seek_empty_packet and test_seek_big_trace from SCRIPT_LIST

Since these files are generated by autoconf, they shouldn't be included
in SCRIPT_LIST, which is the list of scripts to copy from the source
directory to the build directory.  This gets rid of these warnings when
building out of tree:

  cp: cannot stat '/home/simark/src/babeltrace/tests/lib/test_seek_big_trace': No such file or directory
  cp: cannot stat '/home/simark/src/babeltrace/tests/lib/test_seek_empty_packet': No such file or directory

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>