[GPU] Delete unused apps

Deleted Apps

• Basel
• BaselMultiGPU
• BaselNU
• ChannelFlow
• gridGeneratorTest
• MusselOyster
• TGV_3D_GridRef
• TGV_3D_MultiGPU
• wifi/UniformInflow
• WTG_RUB

Bookmark:

• MR: !335 (merged)
• commit: 035cf347
• parents: 6c3af634 ca1f6b12