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/LibHTTP/HttpResponse.cpp

@@ -9,7 +9,7 @@
 
 namespace HTTP {
 
-HttpResponse::HttpResponse(int code, HashMap<DeprecatedString, DeprecatedString, CaseInsensitiveStringTraits>&& headers, size_t size)
+HttpResponse::HttpResponse(int code, HashMap<ByteString, ByteString, CaseInsensitiveStringTraits>&& headers, size_t size)
     : m_code(code)
     , m_headers(move(headers))
     , m_downloaded_size(size)