Remove -funfolding-update-in-place flag documentation

This flag does nothing, and should have been removed ages ago. (GHC
no longer does update-in-place.)

MERGE to 6.8 branch

compiler/main/StaticFlags.hs

@@ -375,7 +375,6 @@ isStaticFlag f =
 	"fruntime-types",
 	"fno-pre-inlining",
 	"fexcess-precision",
-	"funfolding-update-in-place",
 	"static",
 	"fhardwire-lib-paths",
 	"funregisterised",

docs/users_guide/flags.xml

@@ -1346,13 +1346,6 @@
 	      <entry><option>-fno-unfolding-keeness-factor</option></entry>
 	    </row>
 
-	    <row>
-	      <entry><option>-funfolding-update-in-place</option></entry>
-	      <entry>Tweak unfolding settings</entry>
-	      <entry>static</entry>
-	      <entry><option>-fno-unfolding-update-in-place</option></entry>
-	    </row>
-
 	    <row>
 	      <entry><option>-funfolding-use-threshold</option></entry>
 	      <entry>Tweak unfolding settings</entry>

docs/users_guide/using.xml

@@ -1600,24 +1600,6 @@ f "2"    = 2
 	  </listitem>
 	</varlistentry>
 
-	<varlistentry>
-	  <term>
-            <option>-funfolding-update-in-place=<replaceable>n</replaceable></option>
-            <indexterm><primary><option>-funfolding-update-in-place</option></primary></indexterm>
-          </term>
-	  <listitem>
-	    <para>Switches on an experimental "optimisation".
-            Switching it on makes the compiler a little keener to
-            inline a function that returns a constructor, if the
-            context is that of a thunk.
-<programlisting>
-   x = plusInt a b
-</programlisting>
-            If we inlined plusInt we might get an opportunity to use
-            update-in-place for the thunk 'x'.</para>
-	  </listitem>
-	</varlistentry>
-
 	<varlistentry>
 	  <term>
             <option>-funfolding-creation-threshold=<replaceable>n</replaceable></option>: