Revert "Temporarily ensure that the file functions test uses UTF-8"

This reverts commit a44bcb4746 which is not
necessary any more since the fixes to file name conversions in the previous
commit.

tests/file/filefn.cpp

@@ -78,10 +78,6 @@ private:
     wxString m_fileNameNonASCII;
     wxString m_fileNameWork;
 
-#ifndef __DARWIN__
-    wxMBConv* m_convFNOld;
-#endif
-
     wxDECLARE_NO_COPY_CLASS(FileFunctionsTestCase);
 };
 
@@ -98,16 +94,6 @@ CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( FileFunctionsTestCase, "FileFunctionsTest
 
 void FileFunctionsTestCase::setUp()
 {
-    // Under Unix we need to use UTF-8 for the tests using non-ASCII filenames
-    // and this is not necessarily the case because the tests don't call
-    // setlocale(LC_ALL, ""), so ensure it explicitly. This is just a temporary
-    // hack until we find the solution to make the library work with Unicode
-    // filenames irrespectively of the current locale.
-#ifndef __DARWIN__
-    m_convFNOld = wxConvFileName;
-    wxConvFileName = &wxConvUTF8;
-#endif
-
     // Initialize local data
 
     wxFileName fn1(wxFileName::GetTempDir(), wxT("wx_file_mask.txt"));
@@ -137,10 +123,6 @@ void FileFunctionsTestCase::tearDown()
     {
         wxRemoveFile(m_fileNameWork);
     }
-
-#ifndef __DARWIN__
-    wxConvFileName = m_convFNOld;
-#endif
 }
 
 void FileFunctionsTestCase::GetTempFolder()