Use GTEST_DONT_DEFINE_TEST_F to guard TEST_F

The documentation is clear that the FOO we'll be guarding always matches
the spelling of the DONT macro.  A single guard macro should not toggle
more than one implementation macro.

This fixes a regression in 7413280c52.

Relatedly, improve the documentation of the DONT macros to bring the
list of valid FOO values up to date.

googletest/README.md

@@ -203,7 +203,9 @@ add
     -DGTEST_DONT_DEFINE_FOO=1
 
 to the compiler flags to tell GoogleTest to change the macro's name from `FOO`
-to `GTEST_FOO`. Currently `FOO` can be `FAIL`, `SUCCEED`, or `TEST`. For
+to `GTEST_FOO`. Currently `FOO` can be `ASSERT_EQ`, `ASSERT_FALSE`, `ASSERT_GE`,
+`ASSERT_GT`, `ASSERT_LE`, `ASSERT_LT`, `ASSERT_NE`, `ASSERT_TRUE`,
+`EXPECT_FALSE`, `EXPECT_TRUE`, `FAIL`, `SUCCEED`, `TEST`, or `TEST_F`. For
 example, with `-DGTEST_DONT_DEFINE_TEST=1`, you'll need to write
 
     GTEST_TEST(SomeTest, DoesThis) { ... }