Remove unused KF6 Archive component.

The Avogadro:Gui target requires the Qt::Concurrent target to be found.

--- CMakeLists.txt.orig	2026-02-28 11:23:51 UTC
+++ CMakeLists.txt
@@ -89,7 +89,6 @@ find_package(KF6 ${KF_MIN_VERSION} REQUIRED COMPONENTS
 )
 
 find_package(KF6 ${KF_MIN_VERSION} REQUIRED COMPONENTS
-    Archive
     Config
     ConfigWidgets
     CoreAddons
@@ -122,6 +121,10 @@ ecm_set_disabled_deprecation_versions(QT 5.14.0
     KF 6.13
 )
 
+
+if (AvogadroLibs_FOUND)
+  find_package(Qt6Concurrent ${QT_MIN_VERSION} REQUIRED)
+endif()
 
 if (HAVE_OPENBABEL AND AvogadroLibs_FOUND AND Eigen3_FOUND)
   find_package(Qt6OpenGL ${QT_MIN_VERSION} REQUIRED)