Replace folly::writeTo with fmt::print

Summary:
Remove `folly::writeTo` which is untested and virtually unused, replacing
```
folly::writeTo(
    stdout,
    folly::format(...));
```
with
```
fmt::print(...);
```
for better compatibility with C++20 `std::format`.

Reviewed By: yfeldblum

Differential Revision: D26326405

fbshipit-source-id: 598ec5d7906b2d36b20aa63f410a0c2621bc62fa

folly/Format.h

@@ -251,13 +251,6 @@ std::ostream& operator<<(
   return out;
 }
 
-/**
- * Formatter objects can be written to stdio FILEs.
- */
-template <class Derived, bool containerMode, class... Args>
-void writeTo(
-    FILE* fp, const BaseFormatter<Derived, containerMode, Args...>& formatter);
-
 /**
  * Create a formatter object.
  *