refactor(core): Remove unused layer `MadsimLayer` #6799

Job	Run time
build-c-doc	27s
build-cpp-doc	54s
build-dav-server-opendalfs-doc	48s
build-fuse3-opendal-doc	1m 11s
build-haskell-doc	10m 56s
build-java-doc	45s
build-lua-doc	9s
build-nodejs-doc	27s
build-object-store-opendal-doc	1m 25s
build-ocaml-doc	7m 33s
build-python-doc	2m 38s
build-rust-doc	6m 55s
build-unftp-sbe-opendal-doc	2m 36s
build-virtiofs-opendal-doc	1m 42s
build-website	6m 44s
	45m 10s

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