remove browse mode and code that became dead as a result of its removal, because the new plan is to launch the program from the terminal (and terminal navigation is okay)

message-types/input-msg.sml

@@ -22,7 +22,6 @@ struct
   | KEY_CTRL_S
   | KEY_CTRL_L
   | KEY_CTRL_E
-  | KEY_CTRL_O
   | KEY_CTRL_C
   | KEY_ESC
   | NUM of int
@@ -34,6 +33,4 @@ struct
   | KEY_SPACE
   | USE_LAYERS of {tree: LayerTree.t, canvasWidth: int, canvasHeight: int}
   | SQUARES_LOAD_ERROR
-  | FILE_BROWSER_AND_PATH of
-      {fileBrowser: AppType.file_browser_item vector, path: string}
 end