[Tagging] leisure=common replacement for public areas with some trees

[Greg Troxel]

leisure=common seems wrong for two reasons:

  the original notion of town common was land that could be used by all
  and was owned by the town or somehow public.   A bit of land that is
  grass in an urban area does not fit this.

  town commons were about grazing or perhaps a meeting place; calling
  them leisure seems very odd

Agreed with others that if it's just grass then just use landcover.