[libc++][C++03] Remove a few XFAILs in test/libcxx

We've split the libc++ tests into C++03 and non-C++03 tests, so these
XFAILs aren't needed anymore.

Author: philnik777

libcxx/test/libcxx/input.output/file.streams/fstreams/filebuf/traits_mismatch.verify.cpp

@@ -15,8 +15,6 @@
 
 // UNSUPPORTED: no-wide-characters
 
-// XFAIL: FROZEN-CXX03-HEADERS-FIXME
-
 #include <fstream>
 
 std::basic_filebuf<char, std::char_traits<wchar_t> > f;

libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.verify.cpp

@@ -15,8 +15,6 @@
 
 // UNSUPPORTED: no-wide-characters
 
-// XFAIL: FROZEN-CXX03-HEADERS-FIXME
-
 #include <fstream>
 
 std::basic_fstream<char, std::char_traits<wchar_t> > f;