For static analysis, it’s better to keep unused literal nodes.
If simply change `block_append` to fall through, both "unused literal ignored"
and "possibly useless use of a literal in void context" warnings
are shown for the same line. But it’s verbose then remove
"unused literal ignored" warning.

This kind of optimization is already implemented on compile.c.
`compile_block` calls `iseq_compile_each0` with `popped = 1` when NODE_BLOCK
has next.