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/Libraries/LibC/stdlib.cpp

@@ -649,7 +649,7 @@ int ptsname_r(int fd, char* buffer, size_t size)
         return -1;
     }
     memset(buffer, 0, devpts_path_builder.length() + 1);
-    auto full_devpts_path_string = devpts_path_builder.to_deprecated_string();
+    auto full_devpts_path_string = devpts_path_builder.to_byte_string();
     if (!full_devpts_path_string.copy_characters_to_buffer(buffer, size)) {
         errno = ERANGE;
         return -1;