Revert "component/openvpn: version up 2.6.8, for OpenSSL 3.0 compatibility."

because re6stnet only supports OpenVPN 2.4.
This reverts commit 6802867d.

component/openvpn/buildout.cfg

 [buildout]
 extends =
-  ../libcap-ng/buildout.cfg
   ../lzo/buildout.cfg
   ../openssl/buildout.cfg
   ../flex/buildout.cfg
@@ -11,11 +10,10 @@ parts =
 
 [openvpn]
 recipe = slapos.recipe.cmmi
-url = https://build.openvpn.net/downloads/releases/openvpn-${:version}.tar.gz
-version = 2.6.8
-md5sum = 427fe070a4ab9fd78dc64195458dc361
+url = https://swupdate.openvpn.org/community/releases/openvpn-${:version}.tar.xz
+version = 2.4.7
+md5sum = 4ad8a008e1e7f261b3aa0024e79e7fb7
 configure-options =
-  --disable-lz4
   --disable-dependency-tracking
   --disable-plugin-auth-pam
   --enable-iproute2
@@ -23,8 +21,6 @@ environment =
   PATH=${xz-utils:location}/bin:%(PATH)s
   LZO_LIBS=-L${lzo:location}/lib -llzo2
   LZO_CFLAGS=-I${lzo:location}/include
-  LIBCAPNG_LIBS=-L${libcap-ng:location}/lib -lcap-ng
-  LIBCAPNG_CFLAGS=-I${libcap-ng:location}/include
   OPENSSL_LIBS=-L${openssl:location}/lib -lcrypto -lssl
   OPENSSL_CFLAGS=-I${openssl:location}/include
   LDFLAGS =-Wl,-rpath=${lzo:location}/lib -Wl,-rpath=${flex:location}/lib -Wl,-rpath=${openssl:location}/lib