The CellSPU backend is more than experimental, it's dead now...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170201 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 3bbac43..216af87 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -526,7 +526,7 @@
 
 Known problem areas include:
 
-#. The CellSPU, MSP430, and XCore backends are experimental.
+#. MSP430, and XCore backends are experimental.
 
 #. The integrated assembler, disassembler, and JIT is not supported by several
    targets.  If an integrated assembler is not supported, then a system