live-preview: Remove dead code related to design mode #18168

Job	Run time
android	1m 48s
cpp_test_driver (ubuntu-22.04)	6m 45s
cpp_cmake (macos-13, 1.77)	27m 43s
cpp_test_driver (macos-13)	10m 57s
build_and_test (ubuntu-22.04, 1.77)	12m 50s
esp-idf-quick	9m 31s
cpp_cmake (windows-2022, nightly)	10m 43s
cpp_test_driver (windows-2022)	8m 33s
build_and_test (macos-13, stable)	27m 42s
cpp_cmake (ubuntu-22.04, stable)	7m 27s
build_and_test (windows-2022, stable)	13m 41s
ffi_32bit_build	1m 11s
build_and_test (windows-2022, 1.77)	14m 42s
fmt_test	1m 31s
build_and_test (windows-2022, beta, --exclude ffmpeg --exclude gstreamer-player)	14m 8s
mcu (pico-st7789, thumbv6m-none-eabi)	42s
build_and_test (ubuntu-22.04, nightly)	15m 36s
mcu_esp	2m 49s
mcu (stm32h735g, thumbv7em-none-eabihf)	42s
miri	45s
node_test (ubuntu-22.04)	4m 9s
python_test (ubuntu-22.04)	2m 57s
updater_test (0.3.0)	1m 22s
python_test (macos-13)	2m 5s
vsce_build_test	5m 59s
python_test (windows-2022)	2m 50s
node_test (macos-13)	4m 3s
node_test (windows-2022)	7m 38s
format_lint_typecheck / format_lint_typecheck	4m 52s
tree-sitter / tree-sitter-tests	8s
wasm / wasm	4m 28s
docs / docs	8m 4s
wasm_demo / wasm_demo	2m 33s
wasm / build-slintpad	36s
cpp_package_test	2m 29s
	4h 3m 59s

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