For those who need a refresher, Kimberly showed up at Jason's house to tell him that she believed she was the reason for the team's inability to morph, aside from Billy's brief unintentional transformation into the Blue Ranger. Apparently this was because of her perception of herself as a bad person due to the realization that the prank she played on a classmate (which sent her to the same detention period that Jason and Billy were stuck in) had gone too far. Jason attempted to comfort her, saying how just because she did a bad thing didn't mean she was a bad person, and that what she did from here on out was what mattered most. Had the scene continued as originally planned, the two of them would have then kissed, but instead, they were called to meet up with Billy, Zack and Trini, the latter of whom had just been attacked by Rita Repulsa.
Source : http://www.cinemablend.com/news/1640560/why-power-rangers-cut-that-big-jason-and-kimberly-scene