[llvm] [Offload] Remove unnecessary omp CMake target dependencies (PR #149060)

[Shilei Tian via llvm-commits]

shiltian wrote:

It works because a program always links `libomp` and `libomptarget` but we can't say there is no need for a dependency between `libomptarget` and `libomp`.

https://github.com/llvm/llvm-project/pull/149060