Small doc tweak of opt.trust_madvise.

Avoid quoted enabled and disabled because it's a bool type instead of char *.

doc/jemalloc.xml.in

diff --git a/doc/jemalloc.xml.in b/doc/jemalloc.xml.in
index 5c12f1d..fe4ded9 100644
--- a/doc/jemalloc.xml.in
+++ b/doc/jemalloc.xml.in
@@ -972,10 +972,9 @@
           (<type>bool</type>)
           <literal>r-</literal>
         </term>
-        <listitem><para>Do not perform runtime check for MADV_DONTNEED, to
-        check that it actually zeros pages.  The default is
-        <quote>disabled</quote> on linux and <quote>enabled</quote> elsewhere.
-        </para></listitem>
+        <listitem><para>If true, do not perform runtime check for MADV_DONTNEED,
+        to check that it actually zeros pages.  The default is disabled on Linux
+        and enabled elsewhere.</para></listitem>
       </varlistentry>
 
       <varlistentry id="opt.retain">