The mystery of a Tampa couple missing for more than a week has been solved after both were found dead.   First, on Saturday night, Hillsborough County sheriff's deputies discovered the body of 34-year-old Wendy Dusza (DOO-zah) in a storage shed at the Tampa condo where she lived with boyfriend Trevor McGinty.   Then on Sunday, the 30-year-old McGinty apparently killed himself in a hotel room in Gainesville. Police had tracked him there and planned to arrest him for killing Dusza. Authorities believe Dusza had been dead more than a week. Investigators say they don't know why she was killed.