bash: Remove initialization of exported functions.

Why fixing a parser of some feature when the actual feature is rarely used, not POSIX shell compliant and can be even implemented selectively in shell scripts that need it?

IMHO, it's the only sane fix for this vulnerability, because even if the parser is someday "fixed enough" so that most cases are _believed_ to be non-exploitable, the feature itself still allows things such as:

```sh
env echo='() { printf "vulnerable\n"; }' bash -c "echo not vulnerable"
```