remote_to_utf8: cut off part of condition always false

A signed char is never larger than 127.
Revert "remote_to_utf8: cut off part of condition always false"

This reverts commit 1553c70961d05ffeb15780d0d1d58f991d9a6c66.

Some architectures like arm64 and ppc64 have unsigned chars where this
commit will cause problems.
Fix compiler warning in src/iri.c
Assertions are now disabled by default
Fixed typo in testenv/server/http/http_server.py