Remove some dead fields from isolate.h

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index b0996825a244ffd550fc75d4ce42f10546b98a2d..f75c02f677f7bd3a430681bf6ebe60ee3358aadd 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -908,7 +908,6 @@ void CodeStub::GenerateFPStubs(Isolate* isolate) {
   SaveFPRegsMode mode = kSaveFPRegs;
   CEntryStub(isolate, 1, mode).GetCode();
   StoreBufferOverflowStub(isolate, mode).GetCode();
-  isolate->set_fp_stubs_generated(true);
 }