A notice that went up on the P.T. website gives a short, to the point notice of this removal.
The distribution period of "P.T. (Playable Teaser)" on PlayStation®Store will expire on Wednesday, April 29, 2015.
For those still unaware, P.T. was revealed at Gamescom 2014. At the time, nobody had any idea that it was a teaser for the then upcoming Silent Hills from Hideo Kojima and Guillermo Del Toro. It even featured Norman Reedus as the potential main protagonist.
A reason for the game's removal from PSN was not yet given by Konami. However, if I were to take a wild guess, I might say that this could have something to do with it. And the hopes of Silent Hills existing at all become dimmer by the day.
At least until PS4 emulators appear in the far flung future, if at all.