Remove submodule `Express` #220

Job	Run time
Documentation	10m 52s
Julia 1.3 - ubuntu-latest - x64 - push	5m 8s
Julia 1.3 - ubuntu-latest - x86 - push	8s
Julia 1.3 - macOS-latest - x64 - push	8m 47s
Julia 1.3 - windows-latest - x64 - push	19m 24s
Julia 1.6 - ubuntu-latest - x64 - push	4m 20s
Julia 1.6 - ubuntu-latest - x86 - push	8s
Julia 1.6 - macOS-latest - x64 - push	9m 18s
Julia 1.6 - windows-latest - x64 - push	11m 20s
Julia 1.7 - ubuntu-latest - x64 - push	4m 28s
Julia 1.7 - ubuntu-latest - x86 - push	9s
Julia 1.7 - macOS-latest - x64 - push	6m 55s
Julia 1.7 - windows-latest - x64 - push	10m 39s
Julia 1.8 - ubuntu-latest - x64 - push	5m 10s
Julia 1.8 - ubuntu-latest - x86 - push	9s
Julia 1.8 - macOS-latest - x64 - push	7m 33s
Julia 1.8 - windows-latest - x64 - push	11m 50s
Julia nightly - ubuntu-latest - x64 - push	5m 24s
Julia nightly - ubuntu-latest - x86 - push	8s
Julia nightly - macOS-latest - x64 - push	8m 2s
Julia nightly - windows-latest - x64 - push	8m 39s
	2h 18m 31s

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