code: public MockSubnet deleteSubnet(final String subnetId) {
  
          if (subnetId != null && allMockSubnets.containsKey(subnetId)) {
              return allMockSubnets.remove(subnetId);
          }
  
          return null;
      }
docs: Delete Subnet.
  
  @param subnetId
  subnetId to be deleted
  @return Mock Subnet.