Revert "Problems if the json-message contains special characters [...]"

This reverts commit 031afb687097762a139878a04f0b39dbb02d32af.

As per the JSON specification in RFC 7159 section 8.1, "JSON text
SHALL be encoded in UTF-8, UTF-16, or UTF-32". [1]

It is therefore incorrect to apply utf8_encode() function to the data
received from the server since it is already in Unicode by definition.

Fixes 0020350

[1] https://tools.ietf.org/html/rfc7159#section-8.1

Conflicts:
library/adodb
library/phpmailer