fix(build): remove unnecessary GGML_BACKEND_DL flag for windows-gpu b… #257

Job	Run time
linux-cpu-avx512-x86_64 build + test	28s
windows-opencl-x86_64 build + test	2m 19s
linux-opencl-x86_64 build + test	42s
linux-vulkan-arm64 build + test	2m 43s
linux-cpu-avx2-x86_64 build + test	33s
linux-openblas-x86_64 build + test	36s
windows-llamafile-x86_64 build + test	1m 55s
windows-cpu-x86_64 build + test	1m 48s
windows-cpu-avx-vnni-x86_64 build + test	1m 49s
windows-cpu-avx512-x86_64 build + test	1m 53s
windows-cpu-avx2-x86_64 build + test	1m 45s
linux-opencl-arm64 build + test	1m 13s
android-arm64-v8a build	47s
windows-vulkan-x86_64 build + test	2m 7s
linux-cpu-arm64 build + test	31s
ios build	50s
isim build	43s
linux-vulkan-x86_64 build + test	1m 13s
linux-neon-arm64 build + test	30s
macos build + test	54s
windows-gpu-x86_64 build + test	4m 46s
linux-cpu-x86_64 build + test	29s
android-x86_64 build + test	1m 57s
linux-openblas-arm64 build + test	1m 22s
windows-openblas-x86_64 build + test	1m 57s
release	-1s
	35m 49s

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