Due to the expansion of the port of Liverpool in the early 18th century "Liverpool Necropolis (Low Hill Cemetery)" was opened in 1825, at the corner of Everton Road and West Derby Road (formerly Rake Lane) on a site covering approximately five acres. Management was vested in a ‘Committee of Proprietors of Low Hill General Cemetery’ the Trusts being defined in a deed of 9th March 1825. The Necropolis was designed by Architect John Foster Jr (1787-1846) while the grounds were laid out by Mr. Shepherd, Curator of the Botanic Gardens at a cost of £8,000. The much needed cemetery was rapidly filled in the following 70 years with 80,000 burials. The first burial taking place on the 1st February 1825 and was used largely by nonconformists. By 1896, the number of burials in the Necropolis had caused serious unsanitary conditions in the surrounding area which led to the closure of the cemetery for interments on the 31st August 1898. Responsibility for the site was transferred to Liverpool Corporation the following day, and in 1913 the lodges, gates & walls were demolished, monuments and large gravestones removed and the area landscaped with ornamental gardens.
On the 22nd April 1914 the Corporation renamed and re-opened it as Grant Gardens after Alderman J. R. Grant, J.P, chairman of the Corporation Parks and Gardens Committee.

Grant Gardens is the same size as The Necropolis was, and presumably the remains are still there.
There would only have been a reason to remove them if the site was going to be built over.