remove C# 7 speclets.

[BillWagner]

with dotnet/csharpstandard#795, all C# 7.n features have been incorporated into the standard.

Some bug fixes remain, but it's feature complete.

---

Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/operators/arithmetic-operators.md	Arithmetic operators (C# reference)
docs/csharp/language-reference/operators/bitwise-and-shift-operators.md	Bitwise and shift operators (C# reference)
docs/csharp/language-reference/operators/boolean-logical-operators.md	"Boolean logical operators - the boolean and, or, not, and xor operators"
docs/csharp/language-reference/operators/nameof.md	nameof expression (C# reference)

[pkulikov]

@BillWagner I'm currently working on revision of the section about ref locals:
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/declarations#ref-locals

Should I use the terms introduced by the spec ("reference variable" and "referent") in the docs as well? Should we keep "ref local" naming as an alternative (for googling and matching other mentions of that concept in the web now)?

[BillWagner]

@pkulikov

Should I use the terms introduced by the spec ("reference variable" and "referent") in the docs as well? Should we keep "ref local" naming as an alternative (for googling and matching other mentions of that concept in the web now)?

Yes and yes. Thank you.

[CamSoper]

lgtm