test framework: Unset http proxy variables in setupenvironment

This breaks a lot of test cases

Gbp-Dch: ignore

test/integration/framework

@@ -398,6 +398,7 @@ EOF
 	export LC_ALL=C.UTF-8
 	unset LANGUAGE APT_CONFIG
 	unset GREP_OPTIONS DEB_BUILD_PROFILES
+	unset http_proxy HTTP_PROXY https_proxy HTTPS_PROXY
 	msgdone "info"
 }