Convert intltest.cpp to UTF-8 encoding

Don't use Latin-1 for this file, this encoding is obsolete.

No real changes, the only non-ASCII character in this file was in a
comment anyhow.

tests/intl/intltest.cpp

@@ -198,7 +198,7 @@ void IntlTestCase::DateTimeFmtFrench()
 
 #ifdef __WXOSX__
     // Things are difficult to test under macOS as the format keeps changing,
-    // e.g. at some time between 10.10 and 10.12 a new " <EFBFBD> " string appeared in
+    // e.g. at some time between 10.10 and 10.12 a new " à " string appeared in
     // its middle, so test it piece-wise and hope it doesn't change too much.
     CHECK( fmtDT.StartsWith("%A %d %B %Y") );
     CHECK( fmtDT.EndsWith("%H:%M:%S") );