Remove some unused #defines from bytestring.cpp

Only the widestring.cpp file needs these values.

Change-Id: I22e7171af2e9061ac5411102b4055fa698c8e47c
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/83151
Auto-Submit: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxcrt/bytestring.cpp b/core/fxcrt/bytestring.cpp
index c82bf8b..60b2847 100644
--- a/core/fxcrt/bytestring.cpp
+++ b/core/fxcrt/bytestring.cpp
@@ -66,10 +66,6 @@
 static_assert(sizeof(ByteString) <= sizeof(char*),
               "Strings must not require more space than pointers");
 
-#define FORCE_ANSI 0x10000
-#define FORCE_UNICODE 0x20000
-#define FORCE_INT64 0x40000
-
 // static
 ByteString ByteString::FormatInteger(int i) {
   char buf[32];