Remove CS1502 page and redirect to CS1503 page

[BartoszKlonowski]

This pull request closes #43993

It moves the code snippet that was implemented for CS1502 to the error page of CS1503.
Page of CS1503 has no code sample that presents the error while indeed, current code sample presents CS1503 instead of CS1502.

The only problem is that I was unable to reproduce the CS1502 to implement any code sample for the CS1502 page. I also tried to utilize code reported in other websites, but no luck, only CS1503 was given by static analysis.
I also found this:
dotnet/runtime#25176 (comment)
that says that CS1503 will be prioritized over CS1502, but I was unable to find anything else. Still, indeed I was able to reproduce the CS1502 error but only as an exception during runtime, not by error of static analysis.
Due to that, I left the CS1502 error page without a code sample.

---

Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/toc.yml	docs/csharp/language-reference/toc
docs/csharp/misc/cs1503.md	Compiler Error CS1503

[BillWagner]

Hi @BartoszKlonowski

I like what you did here so far. I looked at the source, and CS1502 is now commented out: https://github.com/dotnet/roslyn/blob/main/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs#L683

So, the current version of the compiler won't ever generate this error.

If possible, I'll suggest deleting cs1502, and redirecting it to cs1503, including the F1 and helpviewer keywords. If that's more work than you want for this PR, I'll merge this PR as is and create an issue to remove CS1502.

[BartoszKlonowski]

Hello @BillWagner, thanks for taking a look!
I always prefer to separate implementations (PRs), but since having it done here is what you suggest then I'm totally fine with this 👍
I'll have that covered yet today.

[BillWagner]

Thanks again @BartoszKlonowski

I'll now.