String class: removed deep copy on substring method.

Small code cleanup.

Author: cmaglie

cores/arduino/WString.cpp

@@ -527,11 +527,6 @@ int String::lastIndexOf(const String &s2, unsigned int fromIndex) const
 	return found;
 }
 
-String String::substring( unsigned int left ) const
-{
-	return substring(left, len);
-}
-
 String String::substring(unsigned int left, unsigned int right) const
 {
 	if (left > right) {

cores/arduino/WString.h

@@ -158,7 +158,7 @@ class String
 	int lastIndexOf( char ch, unsigned int fromIndex ) const;
 	int lastIndexOf( const String &str ) const;
 	int lastIndexOf( const String &str, unsigned int fromIndex ) const;
-	String substring( unsigned int beginIndex ) const;
+	String substring( unsigned int beginIndex ) const { return substring(beginIndex, len); };
 	String substring( unsigned int beginIndex, unsigned int endIndex ) const;
 
 	// modification