Merge pull request #1734 from rust-lang/revert-1687-patch-1

Revert "Update function-pointer.md for stabilization of `extended_varargs_abi_support`"

Author: traviscross

Diff for: src/types/function-pointer.md

@@ -52,14 +52,7 @@ function], and the `extern` qualifier indicates it is an [extern function].
 
 r[type.fn-pointer.constraint-variadic]
 Variadic parameters can only be specified with [`extern`] function types with
-these calling conventions:
-* `C`
-* `cdecl`
-* `system`
-* `aapcs`
-* `sysv64`
-* `win64`
-* `efiapi`
+the `"C"` or `"cdecl"` calling convention.
 
 r[type.fn-pointer.attributes]
 ## Attributes on function pointer parameters