dev-libs/open62541: fix encryption backend selection behavior

- The build system supports at most one backend (with preference for
mbedtls over openssl if both are selected). Let's model that with
REQUIRED_USE="?? ( mbedtls openssl )"
- Removal of redundant "encryption" USE flag fixes incorrect
  dependencies when backend USE flags are enabled but the encryption USE
  flag is disabled.

Signed-off-by: Lucio Sauer <watermanpaint@posteo.net>

dev-libs/open62541/metadata.xml

@@ -17,18 +17,15 @@
     systems.
   </longdescription>
   <use>
-    <flag name="encryption">
-      Enable encryption support
-    </flag>
     <flag name="mbedtls">
-      Use mbedtls for encryption
+      Enable encryption support using <pkg>net-libs/mbedtls</pkg>
+    </flag>
+    <flag name="openssl">
+      Enable encryption support using <pkg>dev-libs/openssl</pkg>
     </flag>
     <flag name="pubsub">
       Enable OPC/UA Pub/Sub extensions
     </flag>
-    <flag name="openssl">
-      Use openssl for encryption
-    </flag>
     <flag name="tools">
       Build additional shell tools
     </flag>

dev-libs/open62541/open62541-1.4.2.ebuild

@@ -14,13 +14,13 @@ SRC_URI="https://github.com/${PN}/${PN}/archive/v${PV}.tar.gz -> ${P}.tar.gz"
 LICENSE="MPL-2.0"
 SLOT="0"
 KEYWORDS="~amd64 ~arm64 ~x86"
-IUSE="doc encryption examples mbedtls pubsub openssl tools"
+IUSE="doc examples mbedtls pubsub openssl tools"
 # Requires network access
 RESTRICT="test"
 
 REQUIRED_USE="
 	${PYTHON_REQUIRED_USE}
-	encryption? ( || ( mbedtls openssl ) )
+	?? ( mbedtls openssl )
 "
 
 BDEPEND="
@@ -55,10 +55,8 @@ src_configure() {
 		-DUA_FORCE_WERROR=OFF
 	)
 
-	if use encryption; then
-		use mbedtls && mycmakeargs+=(-DUA_ENABLE_ENCRYPTION=MBEDTLS)
-		use openssl && mycmakeargs+=(-DUA_ENABLE_ENCRYPTION=OPENSSL)
-	fi
+	use mbedtls && mycmakeargs+=(-DUA_ENABLE_ENCRYPTION=MBEDTLS)
+	use openssl && mycmakeargs+=(-DUA_ENABLE_ENCRYPTION=OPENSSL)
 
 	cmake_src_configure
 }