Don't pin falco_rules.yaml to an engine version

Currently, falco_rules.yaml is compatible with versions <= 0.13.1 other
than the required_engine_version object itself, so keep that line
commented out so users can use this rules file with older falco
versions.

We'll uncomment it with the first incompatible falco engine change.

rules/falco_rules.yaml

@@ -16,7 +16,15 @@
 # limitations under the License.
 #
 
-- required_engine_version: 2
+# See xxx for details on falco engine and rules versioning. Currently,
+# this specific rules file is compatible with engine version 0
+# (e.g. falco releases <= 0.13.1), so we'll keep the
+# required_engine_version lines commented out, so maintain
+# compatibility with older falco releases. With the first incompatible
+# change to this rules file, we'll uncomment this line and set it to
+# the falco engine version in use at the time.
+#
+#- required_engine_version: 2
 
 # Currently disabled as read/write are ignored syscalls. The nearly
 # similar open_write/open_read check for files being opened for