delete outdated syntax tests

tests/errors/pep492_badsyntax_async10.pyx

-# mode: error
-# tag: pep492, async
-
-async def genexpr(it):
-    return (await x for x in it)
-
-
-async def listcomp(it):
-    return [await x for x in it]
-
-
-async def setcomp(it):
-    return {await x for x in it}
-
-
-async def dictcomp(it):
-    return {await x:x+1 for x in it}
-
-
-# NOTE: CPython doesn't allow comprehensions either
-
-
-_ERRORS = """
-5:12: 'await' not allowed in generators (use 'yield')
-5:12: 'await' not supported here
-# FIXME: remove when implementing async comprehensions
-5:12: 'yield' not supported here
-"""

tests/errors/pep492_badsyntax_async3.pyx

-# mode: error
-# tag: pep492, async
-
-async def foo():
-    [i async for i in els]
-
-_ERRORS = """
-5:7: Expected ']', found 'async'
-"""