Stop forcing --enable-munmap on MinGW.

This is no longer necessary because of the more general chunk
merge/split approach to dealing with map coalescing.

INSTALL

@@ -150,10 +150,7 @@ any of the following arguments (not a definitive list) to 'configure':
     the virtual memory for later use.  munmap() is disabled by default (i.e.
     --disable-munmap is implied) on Linux, which has a quirk in its virtual
     memory allocation algorithm that causes semi-permanent VM map holes under
-    normal jemalloc operation.  Conversely, munmap() (actually VirtualFree()) is
-    forcefully enabled on MinGW because virtual memory mappings do not
-    automatically coalesce (nor fragment on demand), and extra bookkeeping
-    would be required to track mapping boundaries.
+    normal jemalloc operation.
 
 --disable-fill
     Disable support for junk/zero filling of memory, quarantine, and redzones.

configure.ac

@@ -881,10 +881,6 @@ fi
 ],
 [enable_munmap="${default_munmap}"]
 )
-if test "x$enable_munmap" = "x0" -a "x${maps_coalesce}" = "x0" ; then
-  AC_MSG_RESULT([Forcing munmap to avoid non-coalescing map issues])
-  enable_munmap="1"
-fi
 if test "x$enable_munmap" = "x1" ; then
   AC_DEFINE([JEMALLOC_MUNMAP], [ ])
 fi