Since his Presidency began President Trump has been rolling back (or trying to roll back) many of the actions of President Obama. Sometimes (at least in theory) it is easier (practically if not politically) to do this than other times.
The Deferred Action for Childhood Arrivals (DACA) program allowed undocumented persons who arrived in the United States before age 16 and have lived here since June 15, 2007, to stay, work, and go to school in the United States without facing the risk of deportation for two years with renewals available.
DACA was established through a Department of Homeland Security (DHS) Memorandum during the Obama presidency. Getting rid of a statute requires action by Congress or the U.S. Supreme Court. Getting rid of regulations requires going through the Administrative Procedures Act lengthy notice-and-comment process. Getting rid of an agency memorandum requires issuing a superseding memorandum, which DHS has done.