Delete INVALID_POINTER_VALUE.

I would like to remove it because:
1) it was debug only;
2) there were no null checks for `compHndBBtab`, because it is a dependent variable
so there was no need to ditinguish valid null pointer from a bad invalid pointer;
3) that is the only place where this mechanism was used.

src/coreclr/src/jit/jit.h

@@ -762,12 +762,6 @@ extern int jitNativeCode(CORINFO_METHOD_HANDLE methodHnd,
                          JitFlags*             compileFlags,
                          void*                 inlineInfoPtr);
 
-#ifdef HOST_64BIT
-const size_t INVALID_POINTER_VALUE = 0xFEEDFACEABADF00D;
-#else
-const size_t INVALID_POINTER_VALUE = 0xFEEDFACE;
-#endif
-
 // Constants for making sure size_t fit into smaller types.
 const size_t MAX_USHORT_SIZE_T   = static_cast<size_t>(static_cast<unsigned short>(-1));
 const size_t MAX_UNSIGNED_SIZE_T = static_cast<size_t>(static_cast<unsigned>(-1));

src/coreclr/src/jit/jiteh.cpp

@@ -1411,7 +1411,7 @@ void Compiler::fgRemoveEHTableEntry(unsigned XTnum)
     if (compHndBBtabCount == 0)
     {
         // No more entries remaining.
-        INDEBUG(compHndBBtab = (EHblkDsc*)INVALID_POINTER_VALUE;)
+        compHndBBtab = nullptr;
     }
     else
     {