Game manager tweaks

[tehKaiN]

1. Remove pView field and viewLoad() stuff
   1. This code doesn't work anyway since gamestate struct's view is set to 0
   2. There may be gamestates which don't have their own view - such as pause menu displayed in border on game's main vport.
2. gameDestroy() should call gamePopState() in a loop
   1. Less code to maintain
   2. Speed isn't crucial during gameDestroy()
3. Remove fadeout remnants from code
   1. This should be shifted to gamestate implementation or viewport managers since in multi-viewport view with color-changing copperlist doing palette fade isn't trivial task.

Since @approxit is responsible for game manager, I'd like to see his opinion in the comments.

[tehKaiN]

@approxit ping