parser: drop redundant comparison between alias declaration tree and pattern Since _getalias() explicitly tests the type and name of the pattern tree, we don't need to compare "a.tree == tree" for 'symbol', and "a.tree == tree[:2]" for 'func', where tree is either ('symbol', name) or ('func', ('symbol', name)). This change helps implementing better handling of template aliases. See the subsequent patches for details. The alias.tree field is removed as it is no longer used.