libutil: remove Pool::flushBad

this was never actually used, and bad design in the first place—why
should a bad resource be put back into the idle pool? just drop it.

Change-Id: Idab8774bee19dadae0209d404c4fb86dd4aeba1e

src/libstore/remote-store.cc

@@ -940,11 +940,6 @@ std::optional<TrustedFlag> RemoteStore::isTrustedClient()
     return conn->remoteTrustsUs;
 }
 
-void RemoteStore::flushBadConnections()
-{
-    connections->flushBad();
-}
-
 
 RemoteStore::Connection::~Connection()
 {

src/libstore/remote-store.hh

@@ -161,8 +161,6 @@ public:
 
     std::optional<TrustedFlag> isTrustedClient() override;
 
-    void flushBadConnections();
-
     struct Connection;
 
     ref<Connection> openConnectionWrapper();

src/libutil/pool.hh

@@ -184,16 +184,6 @@ public:
     {
         return state.lock()->max;
     }
-
-    void flushBad()
-    {
-        auto state_(state.lock());
-        std::vector<ref<R>> left;
-        for (auto & p : state_->idle)
-            if (validator(p))
-                left.push_back(p);
-        std::swap(state_->idle, left);
-    }
 };
 
 }

tests/unit/libutil/pool.cc

@@ -65,21 +65,6 @@ namespace nix {
         ASSERT_EQ(pool.capacity(), 0);
     }
 
-    TEST(Pool, flushBadDropsOutOfScopeResources) {
-        auto isGood = [](const ref<TestResource> & r) { return false; };
-        auto createResource = []() { return make_ref<TestResource>(); };
-
-        Pool<TestResource> pool = Pool<TestResource>((size_t)1, createResource, isGood);
-
-        {
-            auto _r = pool.get();
-            ASSERT_EQ(pool.count(), 1);
-        }
-
-        pool.flushBad();
-        ASSERT_EQ(pool.count(), 0);
-    }
-
     // Test that the resources we allocate are being reused when they are still good.
     TEST(Pool, reuseResource) {
         auto isGood = [](const ref<TestResource> & r) { return true; };