Remove TODOs from Codebase

[fubuloubu]

What's your issue about?

There's a number of TODOs in the vyper/ codebase currently.

$ grep TODO -r vyper
vyper/compiler.py:            # TODO: mutation
vyper/parser/constants.py:            # TODO: the previous `if` has no else which will result in this
vyper/parser/context.py:    # TODO location info for errors
vyper/parser/expr.py:    # TODO: Once other refactors are made reevaluate all inline imports
vyper/parser/expr.py:            # TODO: Handle special case of literals and simplify at compile time
vyper/parser/stmt.py:    # TODO: Once other refactors are made reevaluate all inline imports
vyper/parser/stmt.py:                # o.pos = getpos(self.stmt) # TODO: Should this be here like in assign()?
vyper/functions/functions.py:    # TODO: unclosed if/elif clause.  Undefined behavior if `sub.location`
vyper/optimizer.py:    # TODO: this unconditionally returns `False`.  Corresponding optimizer path
vyper/optimizer.py:        # TODO: This block is currently unreachable due to

$ grep TODO -r tests
tests/parser/functions/test_raw_call.py:    # TODO: This one is special

How can it be fixed?

Investigate and remove them.

[charles-cooper]

note: as of c3e43d7b8a2e2236e236b9f23c3a8f9a96de349c, the number of TODOs has only gone up

(vyper) ~/vyper $ git grep TODO | wc
    193    1749   16345