remove do_compare method with optional arguments to have two methods

`virtual bool do_compare( const uvm::uvm_object& rhs,
                           const uvm::uvm_comparer* comparer = NULL ) const `

should be 
`virtual bool do_compare( const uvm::uvm_object& rhs) const `
`virtual bool do_compare( const uvm::uvm_object& rhs, const uvm::uvm_comparer* comparer) const `

