Don't emit synthesized attributes on closure methods

[RikkiGibson]

Follow up to #39226 (comment)

Consider a few lambdas and local functions like the following:

• (Action<dynamic>)(dynamic d) => ...
• void local1(in string s) { ... }
• void local1(params int[] arr) { ... }

For methods like these we synthesize InAttribute, DynamicAttribute, ParamArrayAttribute, etc. so that we can recognize these C# language concepts when we read the methods back in from metadata. But it may not be necessary to do this for local functions or lambdas. There could be a modest size improvement if we stopped emitting these attributes.

This could negatively affect ILSpy's ability to decompile the closures, but this isn't typically something that's extremely important to us.

/cc @jaredpar

[tmat]

The debugger needs these attributes when compiling expressions in EEs, no?