Revert "Prefix error_code with underscore in FastZPP implementation"

Revert "Prefix error_code with underscore in FastZPP implementation"

This reverts commit 6305119a5193d4318add01190ca4afbb49ded102.

This is a source-compatibility break for extensions that define
custom FastZPP macros, such as ext/uv:

https://github.com/bwoebi/php-uv/blob/a983eb17b69f74a45d785ddc6a7bff3d4531b88c/php_uv.c#L75

I don't think that FastZPP was intended to be used this way, but
let's revert this from release branches to avoid extension breakage.