in_sdl: add some debug logging for key events (only if DEBUG_INPUT is defined)

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1108 af15c1b1-3010-417e-b628-4374ebc0bcbd
in_sdl: remove lastKeyDown hack

was no longer needed and was causing issues typing underscores (US keyboard layout) on Linux/SDL2 where SDL_TEXTINPUT is delivered before the SDL_KEYDOWN.

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1109 af15c1b1-3010-417e-b628-4374ebc0bcbd