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/LibThreading/Thread.h

@@ -9,7 +9,7 @@
 
 #include <AK/Assertions.h>
 #include <AK/AtomicRefCounted.h>
-#include <AK/DeprecatedString.h>
+#include <AK/ByteString.h>
 #include <AK/DistinctNumeric.h>
 #include <AK/Function.h>
 #include <AK/Result.h>
@@ -69,7 +69,7 @@ public:
     template<typename T = void>
     Result<T, ThreadError> join();
 
-    DeprecatedString thread_name() const;
+    ByteString thread_name() const;
     pthread_t tid() const;
     ThreadState state() const;
     bool is_started() const;
@@ -80,7 +80,7 @@ private:
     explicit Thread(Function<intptr_t()> action, StringView thread_name = {});
     Function<intptr_t()> m_action;
     pthread_t m_tid { 0 };
-    DeprecatedString m_thread_name;
+    ByteString m_thread_name;
     Atomic<ThreadState> m_state { ThreadState::Startable };
 };
 
@@ -120,7 +120,7 @@ template<>
 struct AK::Formatter<Threading::ThreadState> : AK::Formatter<FormatString> {
     ErrorOr<void> format(FormatBuilder& builder, Threading::ThreadState state)
     {
-        DeprecatedString name = "";
+        ByteString name = "";
         switch (state) {
         case Threading::ThreadState::Detached:
             name = "Detached";