Removed tons of api that we dont absolutely need in GtkCellAreaContext:

Removed tons of api that we dont absolutely need in GtkCellAreaContext:

  - gtk_cell_area_context_get_height_for_width()
  - gtk_cell_area_context_get_width_for_height()
  - gtk_cell_area_context_push_height_for_width()
  - gtk_cell_area_context_push_width_for_height()
  - gtk_cell_area_context_flush_height_for_width()
  - gtk_cell_area_context_flush_width_for_height()
  - Contextual size changed signal

All of these are not really important for the CellArea to operate
and not of any real consequential value to the user (the user can
accumulate the returned values from height-for-width requests
and do as they please with it).