LibCore: Completely drop DeprecatedFile

DeprecatedFile doesn't properly handle I/O or OOM errors, and only
provides a rudimentary interface to reasonably handle it. We have long
since learned how to do it "properly" with ErrorOr<> and similar
interfaces. See also d43a7eae54.

Note that this leaves behind an invocation to DeprecatedFile in
Ladybird/AndroidPlatform.cpp. However, that part of the system has
compilation errors since at least January, and will get removed or
rewritten as part of issue #19085. Let's not wait for this Android port
to remove this deprecated API.

Userland/Libraries/LibCore/CMakeLists.txt

@@ -4,7 +4,6 @@ set(SOURCES
     Command.cpp
     ConfigFile.cpp
     DateTime.cpp
-    DeprecatedFile.cpp
     Directory.cpp
     DirectoryEntry.cpp
     DirIterator.cpp