tests: remove dropin test

This determines the pass/fail of a test based on the execution
of a command.  This is the predecessor of Avocado SIMPLE tests,
and as such, can be removed in favor of the former.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

generic/tests/dropin.py

-import os
-
-from avocado.utils import process
-
-from virttest import data_dir
-
-
-def run(test, params, env):
-    """
-    Run a dropin test.
-    """
-    dropin_path = params.get("dropin_path")
-    dropin_path = os.path.join(data_dir.get_root_dir(), "dropin",
-                               dropin_path)
-    try:
-        process.system(dropin_path, shell=True)
-    except process.CmdError:
-        test.fail("Drop in test %s failed" % dropin_path)