Remove testing/test_modimport.py

testing/test_meta.py ensures this already as a side effect
(+ tests a few more (`__init__.py` files) and should have been
combined with it right away [1].

1: https://github.com/pytest-dev/pytest/pull/4510#discussion_r289123446

Ref: https://github.com/pytest-dev/pytest/commit/eaa05531e
Ref: https://github.com/pytest-dev/pytest/commit/4d31ea831

testing/test_modimport.py

@@ -1,40 +0,0 @@
-import subprocess
-import sys
-
-import py
-
-import _pytest
-import pytest
-
-pytestmark = pytest.mark.slow
-
-MODSET = [
-    x
-    for x in py.path.local(_pytest.__file__).dirpath().visit("*.py")
-    if x.purebasename != "__init__"
-]
-
-
-@pytest.mark.parametrize("modfile", MODSET, ids=lambda x: x.purebasename)
-def test_fileimport(modfile):
-    # this test ensures all internal packages can import
-    # without needing the pytest namespace being set
-    # this is critical for the initialization of xdist
-
-    p = subprocess.Popen(
-        [
-            sys.executable,
-            "-c",
-            "import sys, py; py.path.local(sys.argv[1]).pyimport()",
-            modfile.strpath,
-        ],
-        stdout=subprocess.PIPE,
-        stderr=subprocess.PIPE,
-    )
-    (out, err) = p.communicate()
-    assert p.returncode == 0, "importing %s failed (exitcode %d): out=%r, err=%r" % (
-        modfile,
-        p.returncode,
-        out,
-        err,
-    )