[llvm-objcopy] Remove empty SHT_GROUP sections (#97141)
Currently `llvm-objcopy/llvm-strip` in `--strip-debug` mode doesn't
remove such sections. This behavior can lead to incompatibilities with
GNU binutils (for examples ld.bfd before https://sourceware.org/PR20520
cannot process the object file contains empty .group section).
The ELF object that contains group section with `.debug_*` sections
inside can be obtained by `gcc -g3`.
Fix #97139
