kde-apps/kpimtextedit: Drop unused BUILD_DESIGNERPLUGIN cmake arg

It was removed upstream at some point during KF6 porting.

Closes: https://bugs.gentoo.org/935722
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>

kde-apps/kpimtextedit/kpimtextedit-24.05.2.ebuild

@@ -3,7 +3,6 @@
 
 EAPI=8
 
-ECM_DESIGNERPLUGIN="true"
 ECM_QTHELP="true"
 ECM_TEST="true"
 KFMIN=6.3.0

kde-apps/kpimtextedit/metadata.xml

@@ -8,7 +8,4 @@
 	<upstream>
 		<bugs-to>https://bugs.kde.org/</bugs-to>
 	</upstream>
-	<use>
-		<flag name="designer">Build plugins for <pkg>dev-qt/designer</pkg></flag>
-	</use>
 </pkgmetadata>