Uncomment `specifyuser_spprincipal` usage

[alesan99]

Describe the bug

specify7/specifyweb/backend/businessrules/rules/user_rules.py

Lines 33 to 38 in 6cc0c96

	# TODO: UNCOMMENT THIS. Commented specifically for testing PR https://github.com/specify/specify7/pull/6671
	# for gp in group_principals:
	# cursor.execute(
	# 'insert into specifyuser_spprincipal(specifyuserid, spprincipalid) values (%s, %s)',
	# [user.id, gp.id]
	# )

The code was commented for testing purposes in #6671 but was never uncommented.

Expected behavior
This code should still be present.