Revert "wrealpath: Fail for file/something"

Apparently macOS realpath is broken.

This reverts commit ca1c499069.

src/wutil.cpp

@@ -414,9 +414,9 @@ maybe_t<wcstring> wrealpath(const wcstring &pathname) {
                 // If there is no "/", this is a file in $PWD, so give the realpath to that.
                 narrow_res = realpath(".", tmpbuf);
             } else {
-                // Be sure to include the last "/" to have the penultimate component considered a directory.
-                // Otherwise "file/something" succeeds.
-                narrow_res = realpath(narrow_path.substr(0, pathsep_idx + 1).c_str(), tmpbuf);
+                errno = 0;
+                // Only call realpath() on the portion up to the last component.
+                narrow_res = realpath(narrow_path.substr(0, pathsep_idx).c_str(), tmpbuf);
             }
 
             if (!narrow_res) return none();

tests/realpath.err

@@ -1,3 +1,2 @@
 builtin realpath: /this/better/be/an/invalid/path: No such file or directory
 builtin realpath: .: No such file or directory
-builtin realpath: realpath.out/..: Not a directory

tests/realpath.in

@@ -80,7 +80,4 @@ else
     echo "unexpected pwd-resolved-to-itself failure: $real_path != $PWD" >&2
 end
 
-# Confirm that the penultimate component still needs to be a directory:
-builtin realpath realpath.out/..
-
 exit 0