scripts: remove unneeded fsx-legacy.bat #1558

Job	Run time
linux-newLTS-vanilla--dotnet6	9m 28s
linux-newLTS-github--dotnet-and-xbuild	7m 55s
linux-newLTS-vanilla--newmono	7m 40s
linux-newLTS-github--dotnet-and-msbuild	9m 33s
linux-newLTS-vanilla--stockmono	5m 15s
linux-oldLTS-github--dotnet-and-msbuild	7m 50s
linux-oldLTS-github--dotnet-and-xbuild	7m 13s
linux-oldLTS-vanilla--newmono	6m 43s
linux-oldLTS-vanilla--stockmono	6m 22s
macOS--dotnet6-and-mono	12m 4s
macOS--mono	8m 24s
windows--dotnet6	11m 29s
windows--legacyFramework	21m 15s
sanity-check	1m 2s
publish	0s
	2h 2m 13s

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