Temporarily remove export defer * as x from "x"

tc39#30 and tc39#31, that implement more general "optional/deferred
re-exports" with tree-shaking capabilities, give two different
meaning to `export defer * as x from "x"`:
- in tc39#30, `export defer * as x from "x"` unconditionally loads  `"x"`,
  and defers it's execution until when the namespace is used
- in tc39#31, it only loads `x` if some module is actually importing `{ x }`
  from this one, and then defers its execution

Due to this difference, for now it's better to remove `export defer *`
until its semantics are settlet, together with the other `export defer`/
`export optional` cases. I will include a revert for this commit in
those two PRs.