Remove `ThinClient` from `dos/` #107

Job	Run time
android (ubuntu-20.04, x86_64-linux-android)	2m 57s
android (ubuntu-20.04, aarch64-linux-android)	3m 6s
ios (macos-11, aarch64-apple-ios)	6m 0s
ios (macos-11, x86_64-apple-ios)	7m 3s
android (ubuntu-20.04, i686-linux-android)	3m 4s
ios (macos-11, aarch64-apple-darwin)	6m 16s
android (ubuntu-20.04, armv7-linux-androideabi)	3m 16s
ios (macos-11, x86_64-apple-darwin)	6m 17s
error_reporting	0s
	37m 59s

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