As Dmitry Abt said, it seems that in pg_routing 3.0 it's no longer a function. Not sure what you're trying to do, and I never used this function, but maybe ST_ConcaveHull (or eventually ST_ConvexHull) could do the same job? Or you still have pgr_alphaShapepgr_alphaShape in 3.0, wich seems to be the core function for alpha shapes.
Edit: as JGH said, the signature of the pgr_alphaShape changed, so I edited the link