Small mistakes in microbenchmark code

Going through the Microbenchmarks I notice some small issues: * Microbenchmark 14 `microbenchmarks/indirect-call-index-expression/main.wat` line `25`: Wrong function index inserted into table. Inserted should be `$not-reachable` instead of `$b`. * Microbenchmark 20 `microbenchmarks/indirect-call-index-expr-load-interprocedural-param/main.wat` is missing completely * Microbenchmark 21 `microbenchmarks/indirect-call-index-expr-load-interprocedural-result/main.wat` comment states function id is `$call_indirect` but it is actually `$index`