Remove SDL_ttf from sdl_key{_proxy}

SDL_ttf wasn't used at all. No need to include it.

```
➜  tests git:(incoming) ✗ python runner.py browser.test_sdl_key browser.test_sdl_key_proxy
[Browser harness server on process 65057]

Running the browser tests. Make sure the browser allows popups from localhost.

test_sdl_key (test_browser.browser) ... ok
test_sdl_key_proxy (test_browser.browser) ... ok
[Browser harness server terminated]

----------------------------------------------------------------------
Ran 2 tests in 3.571s

OK
```