build: drop the broken Qt plugin staging for test_dash-qt

The block was gated on QT_IS_STATIC, a variable that is set nowhere, so it ran even for static-Qt depends builds; nothing created the plugins/platforms directory first, so 'cmake -E copy_if_different' produced a regular file named 'platforms'; and Qt would not have searched that location anyway - without a qt.conf it looks in <appdir>/platforms, not <appdir>/plugins/platforms.

It is also unnecessary: the static-Qt case is handled by import_plugins() via qt5_import_plugins a few lines up, and a shared Qt finds qminimal in its own installed plugin directory, which is why the tests pass with the staging broken. Upstream has no equivalent block.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: PastaPastaPasta

src/qt/test/CMakeLists.txt

@@ -39,14 +39,6 @@ if(ENABLE_WALLET)
   )
 endif()
 
-if(NOT QT_IS_STATIC)
-  add_custom_command(
-    TARGET test_bitcoin-qt POST_BUILD
-    COMMAND ${CMAKE_COMMAND} -E copy_if_different $<TARGET_PROPERTY:Qt5::QMinimalIntegrationPlugin,LOCATION_$<UPPER_CASE:$<CONFIG>>> $<TARGET_FILE_DIR:test_bitcoin-qt>/plugins/platforms
-    VERBATIM
-  )
-endif()
-
 add_test(NAME test_bitcoin-qt
   COMMAND test_bitcoin-qt
 )