Update fxjs/README now that context data slots are gone

TBR=dsinclair@chromium.org

Change-Id: I2665f616d451ff7075b63457a91ef264bbde84c9
Reviewed-on: https://pdfium-review.googlesource.com/34610
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/fxjs/README b/fxjs/README
index 85c5edf..6590b58 100644
--- a/fxjs/README
+++ b/fxjs/README
@@ -37,7 +37,3 @@
 four v8::Contexts (JS Global Objects) associated with each document. One is
 used by FXJS and holds objects as described by the js_api_reference.pdf
 specification. The others are used by FXJSE.
-
-FXJS requires that it can find itself whatever the current context might
-be through a v8::Context's slot -- even if one of the FXJSE contexts is
-current.
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