The decommissioning should have been carried out by the Client before the demolition contractor was on site and written confirmation included in the site report as part of the preconstruction information.
BS6187-2011 Code_of_Practice_for_Demolition is what the HSE expect you to work to. It states:-
The health and safety file should include the following information, as appropriate.
a) Description of the works undertaken and site location details.
b) Description of the site as is, including topographical details as necessary.
c) Any known underground residual risks remaining, i.e ground conditions, buried objects, voids and chambers.
d) Known service runs/locations and/or termination points in and around the site.
e) Details of the structural principles and safe working loads for floors and roofs.
f) Remaining proximity hazards for oncoming contractors or users of the site.
g) Water courses, drainage or soakaways remaining.
h) Safe access and egress points, boundaries and security concerns.
i) Any other information deemed relevant.
In addition, all service disconnections, drainage terminations, etc., should be recorded in the health and safety file that is compiled as the work progresses and is usually coordinated on behalf of the client.
As Ian Bell2 said, the risks associated with the sprinklers no longer exist.