Reimplement our no-op utmp.h functions more simply.

Now we're being marked down for our poor coverage, we may as well remove
more broken cruft. Despite the amount of effort that seems to have gone
into pututline(), it wasn't working with the other utmp.h functions (in
particular, utmpname()), and wasn't declared in the header file!

Test: treehugger
Change-Id: I1a583984189c751168c11c01431433f96f8c548b
diff --git a/tests/utmp_test.cpp b/tests/utmp_test.cpp
index 0fa55c7..6d0d6f1 100644
--- a/tests/utmp_test.cpp
+++ b/tests/utmp_test.cpp
@@ -24,8 +24,10 @@
   ASSERT_EQ(-1, login_tty(-1));
 }
 
-TEST(utmp, setutent_getutent_endutent) {
+TEST(utmp, smoke) {
+  ASSERT_EQ(-1, utmpname("hello"));
   setutent();
-  getutent();
+  ASSERT_EQ(NULL, getutent());
   endutent();
+  ASSERT_EQ(NULL, pututline(NULL));
 }