Revert "Add fs.ts to abstract over fs"

This reverts commit 290760874e.

src/fs.ts

@@ -1,35 +0,0 @@
-/**
- * This module exports a `FileSystem` type which corresponds to the interface of the "fs" module.
- *
- * Functions which are parameterised over this type can then be passed a different implementation in tests:
- *
- * ```typescript
- * import * as nodefs from "fs";
- *
- * function foo(fs: FileSystem = nodefs) {
- *   // Uses the real "fs" module by default, but can be given a different implementation.
- * }
- * ```
- *
- * The type can also be constrained to a subset of available operations. For example, in the following
- * case we have a function that only needs `statSync`:
- *
- * ```
- * function bar(fs: FileSystem<"statSync"> = nodefs) {
- *   // This function can only use `statSync`.
- * }
- * ```
- *
- * This is useful to define a clearer interface for what the function does and also only requires stubbing
- * of the relevant functions.
- */
-
-import * as fs from "fs";
-
-/** Represents the names of operations exported from "fs". */
-export type FileOperation = keyof typeof fs;
-
-/** Represents the type of "fs", optionally filtered down to just `Ops`. */
-export type FileSystem<Ops extends FileOperation = keyof typeof fs> = {
-  [Key in Ops]: (typeof fs)[Key];
-};