Clean up file loader callback #17648

Job	Run time
android	2m 14s
cpp_test_driver (ubuntu-22.04)	6m 52s
cpp_cmake (macos-12, 1.77)	11m 51s
cpp_test_driver (macos-12)	7m 13s
build_and_test (ubuntu-22.04, 1.77)	13m 1s
cpp_cmake (windows-2022, nightly)	9m 59s
cpp_test_driver (windows-2022)	9m 44s
build_and_test (macos-12, stable)	29m 54s
cpp_cmake (ubuntu-22.04, stable)	7m 24s
build_and_test (windows-2022, stable)	15m 2s
esp-idf-quick	8m 53s
build_and_test (windows-2022, 1.77)	14m 34s
ffi_32bit_build	1m 15s
build_and_test (windows-2022, beta, --exclude ffmpeg --exclude gstreamer-player)	15m 4s
fmt_test	1m 36s
build_and_test (ubuntu-22.04, nightly)	9m 39s
mcu (pico-st7789, thumbv6m-none-eabi)	31s
mcu (stm32h735g, thumbv7em-none-eabihf)	39s
mcu_esp	2m 33s
miri	46s
node_test (ubuntu-22.04)	3m 9s
node_test (macos-12)	3m 46s
python_test (ubuntu-22.04)	1m 42s
updater_test (0.3.0)	1m 27s
python_test (macos-12)	1m 21s
node_test (windows-2022)	8m 55s
vsce_build_test	5m 25s
python_test (windows-2022)	2m 17s
docs / docs	6m 22s
tree-sitter / tree-sitter-tests	9s
wasm / wasm	4m 2s
wasm_demo / wasm_demo	2m 11s
wasm / lint-slintpad	17s
wasm / build-slintpad	31s
cpp_package_test	2m 47s
	3h 33m 5s

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