Update an outdated comment in the CEntryStub on ARM.

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
diff --git a/src/arm/code-stubs-arm.cc b/src/arm/code-stubs-arm.cc
index 24d10c8a4b06695b06d3923134cdef231f0405fc..f98c877befd7f7e1637c6de49765db0deb0897f9 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -3403,15 +3403,10 @@ void CEntryStub::GenerateCore(MacroAssembler* masm,
 
   __ mov(r2, Operand(ExternalReference::isolate_address()));
 
-
-  // TODO(1242173): To let the GC traverse the return address of the exit
-  // frames, we need to know where the return address is. Right now,
-  // we store it on the stack to be able to find it again, but we never
-  // restore from it in case of changes, which makes it impossible to
-  // support moving the C entry code stub. This should be fixed, but currently
-  // this is OK because the CEntryStub gets generated so early in the V8 boot
-  // sequence that it is not moving ever.
-
+  // To let the GC traverse the return address of the exit frames, we need to
+  // know where the return address is. The CEntryStub is unmovable, so
+  // we can store the address on the stack to be able to find it again and
+  // we never have to restore it, because it will not change.
   // Compute the return address in lr to return to after the jump below. Pc is
   // already at '+ 8' from the current instruction but return is after three
   // instructions so add another 4 to pc to get the return address.