[1177] Remove FIXME comments

As the concerns there seem to be false ones.

src/lib/datasrc/datasrc_messages.mes

@@ -63,6 +63,11 @@ The maximum allowed number of items of the hotspot cache is set to the given
 number. If there are too many, some of them will be dropped. The size of 0
 means no limit.
 
+% DATASRC_DATABASE_COVER_NSEC_UNSUPPORTED %1 doesn't support DNSSEC when asked for NSEC data covering %2
+The datasource tried to provide an NSEC proof that the named domain does not
+exist, but the database backend doesn't support DNSSEC. No proof is included
+in the answer as a result.
+
 % DATASRC_DATABASE_FIND_RECORDS looking in datasource %1 for record %2/%3
 Debug information. The database data source is looking up records with the given
 name and type in the database.

src/lib/datasrc/tests/database_unittest.cc

@@ -1674,15 +1674,12 @@ TYPED_TEST(DatabaseClientTest, NXDOMAIN_NSEC) {
 
 TYPED_TEST(DatabaseClientTest, emptyNonterminalNSEC) {
     // Same as NXDOMAIN_NSEC, but with empty non-terminal
-    //
-    // FIXME: Is the nonexistence of this node really the correct proof
-    // we need?
     shared_ptr<DatabaseClient::Finder> finder(this->getFinder());
 
     this->expected_rdatas_.push_back("empty.nonterminal.example.org. NSEC");
     doFindTest(*finder, isc::dns::Name("nonterminal.example.org."),
                isc::dns::RRType::TXT(), isc::dns::RRType::NSEC(), this->rrttl_,
-               ZoneFinder::NXRRSET, // FIXME: Do we want to have specific code?
+               ZoneFinder::NXRRSET,
                this->expected_rdatas_, this->expected_sig_rdatas_,
                Name("l.example.org."), ZoneFinder::FIND_DNSSEC);