schannel: Removed extended error connection setup flag

According KB975858 this flag may cause problems on Windows 7 and
Windows Server 2008 R2 systems. Extended error information is not
currently used by libcurl and therefore not a requirement.

The flag may improve the SSL-connection shutdown in case of an
error. This means it might be a good improvement in the future.

Fixes bug/issue #1187 - thanks for the report