Remove startup byte[] allocation in EventSource

[stephentoub]

Only occurs once and is then cached, but it's hit on startup, and may as well remove it.

	IL_0000: ldsflda valuetype '<PrivateImplementationDetails>'/'__StaticArrayInitTypeSize=16' '<PrivateImplementationDetails>'::BABB0FF3A59F6738CDF14170DA56230D6528DC9D619C5860288B86A4E3B29D63
	IL_0005: ldc.i4.s 16
	IL_0007: newobj instance void valuetype System.ReadOnlySpan`1<uint8>::.ctor(void*, int32)
	IL_000c: stloc.0

cc: @noahfalk

[noahfalk]

LGTM, thanks Stephen!

[stephentoub]

I had to put the old code back under ifdef to not break the downlevel assembly. What is that library for?

[noahfalk]

My understanding is that ES_BUILD_STANDALONE define is to build this nuget package, which was offered as an out-of-band release vehicle for some EventSource functionality before it was available in the official runtime release. At this point I don't think we release this thing any more and I doubt there is any purpose to keeping the define or the project in our source.

@brianrob - does that sound right?

[stephentoub]

We're still building https://github.com/dotnet/runtime/tree/master/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist. If we can remove that, great :)

[brianrob]

It's actually this package: https://www.nuget.org/packages/Microsoft.Diagnostics.Tracing.EventSource.Redist/

You're right that it's an out-of-band release vehicle for EventSource - specifically for desktop, since it's hard to get fixes to desktop customers in a timely manner. I would recommend not getting rid of this, as the problem of shipping fixes to desktop customers isn't likely to go away, and this is a thing that comes up every once and while, and is always a high-priority thing when it comes up. The last time it was a big deal, we didn't have a way to produce a package, and thus I ended up doing the work to add it here.