forgetest: forgectrl's test scratch trees leave the repository, and the two still written are ignored

forgetest/cool-flow-test/, forgetest/super-test/ and
forgetest/cool-fanwrite-test/ (46 files) are the scratch trees that
forgectrl's cool_flow_test and super_test, and the fan-write test that
cool_flow_test took in, write in the directory they run from: fake
sysfs attributes, a cooling.state verdict, an empty dev/glowforge.
447f902 committed them beside a change to suite/exthost.py that needs
none of them. Nothing reads them: forgetest.bb fetches forgetest/LICENSE,
forgetest/forgetest/, forgetest/forgetest.init and scripts/bench/, no
manifest component holds them, and no other file of the repository
names them.

The three trees go. forgetest/.gitignore ignores the two that the
forgectrl tests still write, so a run from this directory cannot stage
them again.

Proof: git grep finds the three directory names nowhere else in the
repository. forgetest-ci "Unit tests" (`python -B -m unittest discover
-s tests`) on this tree with meta-openglow beside it, on Ubuntu 24.04
with python 3.12 in a private PID namespace: 357 tests OK, with
test_image.py's account-render case skipped there (it makes a namespace
through sudo -n); test_image.py on its own outside the namespace: 29
tests OK. pyflakes reports no undefined name. The coverage lint on the
tree manifest from the recipe pins reports 0 uncovered paths, 0
host-tested row problems, 43 tests.

Acceptance: none. forgetest is dev-only, and the trees are outside
forgetest.bb's sources, every manifest component and every layer
content hash.

forgetest/.gitignore

@@ -0,0 +1,4 @@
+# The scratch trees forgectrl's cool_flow_test and super_test write in the
+# directory they run from
+/cool-flow-test/
+/super-test/