revert forcing system-odbc on MAc as Maverick dropped system support

We prolly need to look at iODBC and how to carry the headers
as 'external'
Note the dylib for runtime are still in 10.9

Change-Id: I6cad2b90fcb61b5787c0599e40d48a74b8ff917a

configure.ac

@@ -8797,7 +8797,7 @@ dnl ===================================================================
 dnl Check for system odbc
 dnl ===================================================================
 AC_MSG_CHECKING([which odbc headers to use])
-if test "$with_system_odbc" = "yes" -o "$_os" = Darwin ; then
+if test "$with_system_odbc" = "yes" ; then
     AC_MSG_RESULT([external])
     SYSTEM_ODBC_HEADERS=TRUE