Remove KOKKOSTOOLS_LIBRARY_MODE

[masterleinad]

KOKKOSTOOLS_LIBRARY_MODE isn't a CMake variable (and not documented) and there doesn't seem much of an advantage over using the implicit BUILD_SHARED_LIBS option. Note that kp_add_library expects all extra arguments to be source files anyway so specifying KOKKOSTOOLS_LIBRARY_MODE wouldn't actually work.

[vlkale]

Looks OK to me especially if KOKKOSTOOLS_LIBRARY_MODE

is not doing anything anyway given what kp_add_library expects. Note that the sampler and filter are the only two utilities in Kokkos Tools, and I wonder why this was done just for Kokkos Tools.

In any case, I am good with removing it.