Believe it or not, there was a time when there were zero superhero shows on TV. Now there are so many that they don’t all fit on TV. Even though most of The CW’s lineup is DC Comics adaptations, there isn’t room for all of them. “Titans,” which premiered last fall, and “Doom Patrol,” which launched last month, are both on the DC Universe streaming channel. The pilot episodes are available for free through March 29.