[Libomptarget][NFCI] Remove caching of created ELF files (#76080)

Summary:
We currently keep a cache of created ELF files from the relevant images.
This shouldn't be necessary as the entire ELF interface is generally
trivially constructable and extremely cheap. The cost of constructing
one of these objects is simply a size check and writing a pointer to the
underlying data. Given that, keeping a cache of these images should not
be necessary overall.