A stinging thorn in Sony's side has been removed. Daniel Loeb has sold his stake in the company. The activist investor confirmed in a letter to Third Point investors that his hedge fund has exited an equity position in the conglomerate after earning at 20 percent return on investment. Loeb notoriously lobbied for Sony to spin off its entertainment unit, harshly criticizing the studio for summer flops "After Earth" and "White House Down." The company declined to act on Loeb's suggestions but cut…