Interval order COME_FROMs in Python3

This bug had possibly caused lots of grammar pollution which may need
addressing.

We want to process COME_FROMs to the same offset to be in *descending*
order so we have the larger range or biggest instruction interval
last. (I think they are sorted in increasing order, but for safety
we sort them). That way, specific COME_FROM tags will match up
properly. For example, a "loop" with an "if" nested in it should have
the "loop" tag last so the grammar rule matches that properly

Adjust Python 3 grammar for more COME_FROM -> COME_FROM_LOOP. And
remove optional COME_FROM_LOOP where possible. Previously, the
optional-ness was a result of inner nestings gobbling up the
COME_FROM.

We'll probably want to go back and fix this up in Python2.

uncompyle6/parsers/parse2.py

@@ -94,27 +94,6 @@ class Python2Parser(PythonParser):
 
         stmt ::= exec_stmt
 
-        stmt ::= assert
-        stmt ::= assert2
-        stmt ::= ifstmt
-        stmt ::= ifelsestmt
-
-        stmt ::= whilestmt
-        stmt ::= while1stmt
-        stmt ::= whileelsestmt
-        stmt ::= while1elsestmt
-        stmt ::= forstmt
-        stmt ::= forelsestmt
-        stmt ::= trystmt
-        stmt ::= tryelsestmt
-        stmt ::= tryfinallystmt
-        stmt ::= withstmt
-        stmt ::= withasstmt
-
-        stmt ::= del_stmt
-        del_stmt ::= DELETE_FAST
-        del_stmt ::= DELETE_NAME
-        del_stmt ::= DELETE_GLOBAL
         del_stmt ::= expr DELETE_SLICE+0
         del_stmt ::= expr expr DELETE_SLICE+1
         del_stmt ::= expr expr DELETE_SLICE+2