fix: Deno.remove() to properly remove dangling symlinks (denoland#3860)

For some reason, the unit tests for Deno.remove() were not being imported to 
unit_tests.ts and, consequently, not being executed. Thus, I imported them, 
refactored some existent ones and wrote new ones for the symlink removal case.

Since the creation of a symlink is not implemented for Windows yet, assertions
that consider this state were added when the tests are executed in this OS.

cli/js/remove.ts

@@ -6,7 +6,7 @@ export interface RemoveOption {
   recursive?: boolean;
 }
 
-/** Removes the named file or directory synchronously. Would throw
+/** Removes the named file, directory or symlink synchronously. Would throw
  * error if permission denied, not found, or directory not empty if `recursive`
  * set to false.
  * `recursive` is set to false by default.
@@ -17,7 +17,7 @@ export function removeSync(path: string, options: RemoveOption = {}): void {
   sendSync(dispatch.OP_REMOVE, { path, recursive: !!options.recursive });
 }
 
-/** Removes the named file or directory. Would throw error if
+/** Removes the named file, directory or symlink. Would throw error if
  * permission denied, not found, or directory not empty if `recursive` set
  * to false.
  * `recursive` is set to false by default.