Make funcs telling whether to log in cache client, announcer inline.

And remove one unused such function.

src/cache/announcer.cpp

@@ -61,7 +61,7 @@ struct Announcer::Loop {
         , entries(ex)
     { }
 
-    static bool debug() { return logger.get_threshold() <= DEBUG; }
+    inline static bool debug() { return logger.get_threshold() <= DEBUG; }
 
     Entries::iterator find_entry_by_key(const Key& key) {
         for (auto i = entries.begin(); i != entries.end(); ++i) {

src/cache/client.cpp

@@ -97,8 +97,7 @@ struct Client::Impl {
     std::unique_ptr<DhtGroups> _dht_groups;
 
 
-    static bool log_debug() { return logger.get_threshold() <= DEBUG; }
-    static bool log_info() { return logger.get_threshold() <= INFO; }
+    inline static bool log_debug() { return logger.get_threshold() <= DEBUG; }
 
     Impl( shared_ptr<bt::MainlineDht> dht_
         , util::Ed25519PublicKey& cache_pk