Backend.NetStandard: remove project #2501

Job	Run time
linux20-github	5m 2s
linux20-vanilla--stockmono	4m 14s
linux20-github--newmono	5m 46s
linux20-vanilla--newmono	10m 42s
linux22-github--newmono	5m 32s
linux22-github	4m 19s
linux22-vanilla--newmono	10m 26s
linux22-vanilla--stockdotnet6	7m 6s
linux22-vanilla--stockdotnet6-and-newmono	6m 29s
linux22-vanilla--stockdotnet6-and-stockmono	5m 29s
linux22-vanilla--stockmono	7m 1s
macOS--dotnet6-and-mono	7m 44s
macOS--mono	13m 49s
windows--dotnet6	9m 26s
windows--legacyFramework	16m 35s
conventions	0s
snap_pkg	0s
	1h 59m 40s

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