curl: DEPENDS on libidn2 (not libidn)

Since v7.51.0, libidn2 is the only available option, libidn
support was dropped.
The configure option was renamed as of v7.53.0

Therefore, curl unconditionally tries to build against libidn2,
which in particular is a problem for curl-native, as that might
or might not build against the build-machine's libidn2 now,
which furthermore causes problems when trying to share sstate
between multiple build machines.

We therefore see the following in the config log:
    ...
    checking whether to build with libidn2... (assumed) yes
    ...
    checking for libidn2 options with pkg-config... no
    configure: IDN_LIBS: "-lidn2"
    configure: IDN_LDFLAGS: ""
    configure: IDN_CPPFLAGS: ""
    configure: IDN_DIR: ""
    checking if idn2_lookup_ul can be linked... yes
    checking idn2.h usability... yes
    checking idn2.h presence... yes
    checking for idn2.h... yes
    ...
      IDN support:      enabled (libidn2)
    ...
even though this recipe tries to disable that.

While libidn2 isn't available in OE, this change at least:
* prevents curl-native to silently build against libidn2 if
  that is installed on build machine, even if not requested
* alerts people who use the PACKAGECONFIG option that it's
  not actually doing what they intend to do

(From OE-Core rev: 705eaea991622bdbb2ee83eefa8df8e665e3efe4)

Signed-off-by: André Draszik <andre.draszik@jci.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/curl/curl_7.58.0.bb

@@ -34,7 +34,7 @@ PACKAGECONFIG[imap] = "--enable-imap,--disable-imap,"
 PACKAGECONFIG[ipv6] = "--enable-ipv6,--disable-ipv6,"
 PACKAGECONFIG[ldap] = "--enable-ldap,--disable-ldap,"
 PACKAGECONFIG[ldaps] = "--enable-ldaps,--disable-ldaps,"
-PACKAGECONFIG[libidn] = "--with-libidn,--without-libidn,libidn"
+PACKAGECONFIG[libidn] = "--with-libidn2,--without-libidn2,libidn2"
 PACKAGECONFIG[libssh2] = "--with-libssh2,--without-libssh2,libssh2"
 PACKAGECONFIG[pop3] = "--enable-pop3,--disable-pop3,"
 PACKAGECONFIG[proxy] = "--enable-proxy,--disable-proxy,"