Everywhere: Rename {Deprecated => Byte}String

This commit un-deprecates DeprecatedString, and repurposes it as a byte
string.
As the null state has already been removed, there are no other
particularly hairy blockers in repurposing this type as a byte string
(what it _really_ is).

This commit is auto-generated:
  $ xs=$(ack -l \bDeprecatedString\b\|deprecated_string AK Userland \
    Meta Ports Ladybird Tests Kernel)
  $ perl -pie 's/\bDeprecatedString\b/ByteString/g;
    s/deprecated_string/byte_string/g' $xs
  $ clang-format --style=file -i \
    $(git diff --name-only | grep \.cpp\|\.h)
  $ gn format $(git ls-files '*.gn' '*.gni')

Userland/Utilities/rmdir.cpp

@@ -51,7 +51,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
         for (size_t i = path_parts.size() - 1; i > 0; --i) {
             auto current_path_parts = path_parts.span().slice(0, i);
-            LexicalPath current_path { DeprecatedString::join('/', current_path_parts) };
+            LexicalPath current_path { ByteString::join('/', current_path_parts) };
             if (!remove_directory(current_path.string()))
                 break;
         }