OutdatedBlocker: update from 2 years -> 4 years

2 years is too aggressive IMHO. See de65ca7b4a3f3a68b65b56e2dcaf6e511d3a3443
for a recent example of this in ::gentoo but there's been plenty of such
cases in #gentoo on IRC where we got users upgrading fine but they became
unstuck by a removed blocker.

Such blockers are really cheap and the purpose of the warning is really
to remove ancient cruft rather than actually obstruct people upgrading
systems where it's viable.

Note that it's especially problematic because of the current behaviour
of python-exec where emerge won't be able to resume if python-exec got
updated but portage hasn't yet been rebuilt w/ new PYTHON_TARGETS.

(... because if any interruption occurs, it can be fatal.)

Bug: https://bugs.gentoo.org/916498

src/pkgcheck/checks/metadata.py

@@ -995,7 +995,7 @@ def feed(self, pkg):
 
 
 class OutdatedBlocker(results.VersionResult, results.Info):
-    """Blocker dependency removed at least two years ago from the tree.
+    """Blocker dependency removed at least four years ago from the tree.
 
     Note that this ignores slot/subslot deps and USE deps in blocker atoms.
     """
@@ -1061,7 +1061,7 @@ def feed(self, pkg):
                         removal = max(x.time for x in matches)
                         removal = datetime.fromtimestamp(removal)
                         years = (self.today - removal).days / 365
-                        if years >= 2:
+                        if years >= 4:
                             outdated_blockers[attr].add((atom, round(years, 2)))
                     else:
                         nonexistent_blockers[attr].add(atom)

tests/checks/test_metadata.py

@@ -1098,8 +1098,8 @@ def test_outdated_blockers(self):
             self.init_check(future=days)
             self.assertNoReport(self.check, self.source)
 
-        # blocker was removed at least 2 years ago
-        for days, years in ((730, 2), (1825, 5)):
+        # blocker was removed at least 4 years ago
+        for days, years in ((1460, 2), (1825, 5)):
             self.init_check(future=days)
             r = self.assertReport(self.check, self.source)
             expected = metadata.OutdatedBlocker(