[libcxx] [test] Fix comment typos, strip trailing whitespace.

No functional change, no code review.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292434 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/meta/meta.unary/meta.unary.prop/is_literal_type.pass.cpp

@@ -77,7 +77,7 @@ int main()
 #endif
 
 // Before C++14, void was not a literal type
-// In C++14, cv-void is is a literal type
+// In C++14, cv-void is a literal type
 #if TEST_STD_VER < 14
     test_is_not_literal_type<void>();
 #else