LOS ANGELES (Reuters) - Pop star Justin Bieber struck back at his critics on Thursday, denouncing the "countless lies" written about him after a week in which he canceled a concert, collapsed on stage and had a run-in with paparazzi. In a lengthy posting on his Instagram profile, the 19-year-old singer said he was not going into rehab, contrary to some media speculation, and felt he had done nothing to deserve the negative press surrounding his European tour. "Everyone in my team has been telling me, 'keep the press happy' but I'm tired of all the countless lies in the press right now. ...