change "evaluating file" logs to debug

I can't imagine wanting this unless you are debugging something (in
which case it's very useful)

Change-Id: I90c6f182c18486e9f6b15a59379bbb8e88fb8e7f

src/libexpr/eval.cc

@@ -1115,7 +1115,7 @@ void EvalState::evalFile(const SourcePath & path_, Value & v, bool mustBeTrivial
         return;
     }
 
-    printTalkative("evaluating file '%1%'", resolvedPath);
+    debug("evaluating file '%1%'", resolvedPath);
     Expr * e = nullptr;
 
     auto j = fileParseCache.find(resolvedPath);