Revert "Add bitset module in standard"

This reverts commit 7b4ef2df0064875c3e13deac0960296d3ac49849.
Revert "Add bitset module in standard"

This reverts commit 6c829cdd5ad02bdc817940fccb5188427dfa0104.
Revert "Add bitset in standard"

This reverts commit 7d64c570ed9ccce1ceb520208a0de10adff651c4.

Conflicts:
	lib/standard/standard.nit