win32: remove libcurl

win32: remove libcurl

The Windows client does not use libcurl for anything. Remove it to
simplify the build process.

Note, if we ever add libcurl back on Windows, we should disable unused
protocols to harden the build:

  --disable-ftp --disable-ldap --disable-ldaps --disable-rtsp \
  --disable-dict --disable-telnet --disable-tftp --disable-pop3 \
  --disable-imap --disable-smb --disable-smtp --disable-gopher \
  --disable-mqtt --disable-manual --disable-ntlm

Signed-off-by: Ken Dreyer <kdreyer@redhat.com>