cmake: always link to packaged libbpf if CMAKE_USE_LIBBPF_PACKAGE is set (#3210)

Some of the executables still link to the local static versions
even if the user requested CMAKE_USE_LIBBPF_PACKAGE. Fix this by
using bcc-shared-no-libbpf more widely if the variable is set.

Skip the git submodule and the extraction commands if the user
set CMAKE_USE_LIBBPF_PACKAGE