How does one remove the adhesive 'no more nails' from a shelf and wall?

I put up a dado rail many years ago, when ';no nails '; had just come on the market. The shop owner told me that if I ever removed it I would have to have the wall replastered.How does one remove the adhesive 'no more nails' from a shelf and wall?
Hammer and wood chisel ,Very carefully the wall,Shelf an old plane.Or sandpaper.How does one remove the adhesive 'no more nails' from a shelf and wall?
Scrape it off and fill in after as it will leave a big mess.
small chisel





then polyfiller





sandpaper on shelf
try some tar n glue remover avalable from a motorist diy shop
WD-40
hammer