Address compilation warnings

[FlorianReiss]

a non-exhaustive list of compilations warning

• nvcc warning : The 'compute_20', 'sm_20', and 'sm_21' architectures are deprecated, and may be removed in a future release
• src/PDFs/physics/resonances/Spline.cu(19): warning: variable "pwa_coefs_idx" was declared but never referenced
• #warning "host_defines.h is an internal header file and must not be used directly. This file will be removed in a future CUDA release. Please use cuda_runtime_api.h or cuda_runtime.h instead.
• include/goofit/PdfBase.h(36): warning: parameter "oblist" was declared but never referenced
• include/goofit/PdfBase.h(36): warning: parameter "varlist" was declared but never referenced
• include/goofit/PdfBase.h(59): warning: parameter "args" was declared but never referenced
• src/PDFs/PdfBase.cu(167): warning: a __device__ variable "GooFit::d_function_table" cannot be directly read in a host function
• src/PDFs/PdfBase.cu(234): warning: a __device__ variable "GooFit::d_function_table" cannot be directly read in a host function
• src/PDFs/physics/resonances/RhoOmegaMix.cu:36:16: warning: unused variable ‘m’