Back out convertToLowerCase function

It brought in an OSG dependency; we'll just use boost::to_lower_copy instead.

simgear/misc/strutils.cxx

@@ -25,8 +25,6 @@
 
 #include "strutils.hxx"
 
-#include <osgDB/FileNameUtils> // for convertToLowerCase
-
 using std::string;
 using std::vector;
 
@@ -185,12 +183,5 @@ namespace simgear {
 	    return do_strip( s, BOTHSTRIP );
 	}
 
-  string convertToLowerCase(const string& str)
-  {
-    // proxy onto osgDB - easy to reimplement here, but let's avoid
-    // code duplication for the moment.
-    return osgDB::convertToLowerCase(str);
-  }
-
     } // end namespace strutils
 } // end namespace simgear

simgear/misc/strutils.hxx

@@ -79,9 +79,6 @@ namespace simgear {
 	split( const std::string& s,
 	       const char* sep = 0,
 	       int maxsplit = 0 );
-
-
-  std::string convertToLowerCase(const std::string& str);
   
   } // end namespace strutils
 } // end namespace simgear