Revert "Add CURL_WRAPPERS_ENABLE constant"

This reverts commit d7f709a032a40cb475042b43db07a4698a2488b7.
Since wrappers are deleted from 5.5, no point in adding this constant.
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  Revert "Add CURL_WRAPPERS_ENABLE constant"

Conflicts:
	ext/curl/interface.c