interpreter: simplify checks in declare_dependency
interpreter: simplify checks in declare_dependency

Both dependencies.ExternalLibrary and dependencies.InternalDependency are
subclasses of dependencies.Dependency, no need to list them separately.

Signed-off-by: Paolo Bonzini <69d3ebcf5ee4e7f05a50dc23cd96655b730804b4@redhat.com>

mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson