Brian Steinberg Senior TV Editor One of the most coveted jobs in television is quickly becoming one of the hardest to keep filled. Taylor Tomlinson is the latest participant in a lengthening parade of comics and talk-show hosts who have decided that a perch in late-night TV is just not for them. Tomlinson announced Wednesday that she would leave the two-season-old “After Midnight” on CBS despite the offer of a third cycle this fall and the backing of Stephen Colbert, who hosts “The Late Show” an hour before her program airs.