He had not wanted to delete the solar system. It had not been voluntarily.
The Doctor had to leave him, and he had to forget his travels. The Doctor had seen it necessary; afraid he would not be able to stand it. To grasp being back home, where everything would be boring and dull and meaningless. The Doctor needed him to keep living. He had been a brilliant companion, but the Doctor was getting anxious and selfish. He could not keep on the man any longer - what if the next trip would be the one, where his companion would die?
Of course, Sherlock Holmes was a clever man, and most of his knowledge had returned to him slowly. Everything he had learned from the Doctor, but he had never remembered the Doctor himself or the aliens, the monsters or the times he had visited
One day, inevitably, everything had gone wrong. The day had been brilliant; they had saved the world, and they had celebrated, when the Doctor got a sad look upon his face.
And then he touched Sherlock's face. The Doctor's long fingers embraced the tall Detectives face, and taken all the memories out.
He had returned him to 221b, where Mrs. Hudson had helped him drag him up the stairs, and put him on the couch.
He had not thought about it, since John had asked him about the solar system. And since then, both John and he, himself, had caught him looking up at the stars.