remove unused functions, fix tiny lexing bug

before this change, the parser would parse 14.a() as a method call, but
would parse 14.ø() as the floating-point number 14. followed by a function
call. This is because it was checking is_alpha, rather than ident_start,
and was therefore wrong with respect to unicode.
remove unneeded parser functions

the "looking_at_struct_literal" function (sp?) existed to distinguish
blocks from struct literals (and looked fragile as heck, too). Now that
all structs require a preceding identifier (no more structural records),
this function was unnecessary.
hard to read the implied double negative
fix for parsing x() as identifier pattern
needs_comma was always true
rename parse_class_item to parse_struct_decl_field

two problems with the old name: they're not called classes any more, and
the word "item" has a specific connotation in the parser
rename parse_single_class_item as well
remove obsolete semicolon from list of suggestions
rename parse_instance_var to parse_name_and_ty

the name no longer made sense. perhaps this could just be inlined.
remove 3-line used-once function
s/parse_purity/parse_unsafety
removed unneeded argument to parse_record
s/one_tuple/trailing_comma (more accurate name)
parser comments
removed old type dispatch test
deleted two tests intended to test RUST_CC_ZEAL, an apparently defunct flag for the cycle collector
remove (non-parsing) test related to impl d for d feature
this issue is a dup of another one that has a correct test case

this test case has rotted wrt modern syntax. fortunately, this issue
was a dup of another one, and that one still ICEs.
This test case is obsolete for two reasons

First, it refers to a feature (trait bounds on type parameters) that's
apparently no longer in the language. Second, if I understand the issue
correctly, it should never have been a "run-pass" test because it was
supposed to fail.
changed to impl trait for type stx