That deduction has expired.
Last year, Congress made tax changes after the tax filing season started. TurboTax added this comment in case they did it again for tax year 2018, but so far, no changes have been made.
The deduction for mortgage insurance has been eliminated.
According to the IRS:
"The entire list of expired provisions is below....
-
Premiums for mortgage insurance deductible as interest that is qualified residence interest (sec. 163(h)(3))"
https://www.irs.gov/forms-pubs/legislative-impact-on-tax-forms