[1781] small editorial/style fixes: updated comment and use unnamed namespace.

the previous "TODO" comment was a leftover when I moved it from the datasrc
test.  also moved the callback function to the unnamed namespace as it
doesn't have to be referrable from others.

src/lib/testutils/dnsmessage_test.cc

@@ -86,10 +86,8 @@ matchRdata(const char*, const char*,
     }
     return (::testing::AssertionSuccess());
 }
-}
 
-// TODO: maybe we should share this stuff
-// A helper callback of masterLoad() used in InMemoryZoneFinderTest.
+// A helper callback of masterLoad() used by textToRRset() below.
 void
 setRRset(RRsetPtr rrset, RRsetPtr* rrsetp) {
     if (*rrsetp) {
@@ -98,6 +96,7 @@ setRRset(RRsetPtr rrset, RRsetPtr* rrsetp) {
     }
     *rrsetp = rrset;
 }
+}
 
 RRsetPtr
 textToRRset(const string& text_rrset, const RRClass& rrclass) {