Remove USE_UNORDERED_MAP because it has bit-rotted.

Trying to compile with `-DUSE_UNORDERED_MAP` produces lots of compiler errors
like these, because of missing `std::hash` specializations.
Also, `#define unordered_map map` is just evil!

```
./nonisotropic.cpp:875:36: note: in instantiation of template class 'std::__1::unordered_map<hr::nilv::mvec, hr::heptagon *,
      std::__1::hash<hr::nilv::mvec>, std::__1::equal_to<hr::nilv::mvec>, std::__1::allocator<std::__1::pair<const hr::nilv::mvec, hr::heptagon
      *> > >' requested here
    unordered_map<mvec, heptagon*> at;
                                   ^

./nonisotropic.cpp:239:58: note: in instantiation of template class 'std::__1::unordered_map<std::__1::pair<hr::heptagon *, hr::heptagon *>,
      hr::heptagon *, std::__1::hash<std::__1::pair<hr::heptagon *, hr::heptagon *> >, std::__1::equal_to<std::__1::pair<hr::heptagon *,
      hr::heptagon *> >, std::__1::allocator<std::__1::pair<const std::__1::pair<hr::heptagon *, hr::heptagon *>, hr::heptagon *> > >'
      requested here
    unordered_map<pair<heptagon*, heptagon*>, heptagon*> at;
                                                         ^

./nonisotropic.cpp:457:49: error: no matching member function for call to 'iadj'
      while(h1->distance < h2->distance) back = iadj(h2, down) * back, h2 = h2->cmove(down);
                                                ^~~~
cell.cpp:42:15: note: candidate function not viable: no known conversion from 'hr::sn::hrmap_solnih' to 'hr::hrmap' for object argument
  transmatrix iadj(heptagon *h, int d) {
              ^
cell.cpp:41:22: note: candidate function not viable: no known conversion from 'hr::sn::hrmap_solnih' to 'hr::hrmap' for object argument
  struct transmatrix iadj(cell *c, int i) { cell *c1 = c->cmove(i); return adj(c1, c->c.spin(i)); }
                     ^
```

euclid.cpp

@@ -100,7 +100,7 @@ EX namespace euc {
     /** ? */  
     intmatrix inverse_axes;
     /** for canonicalization on tori */
-    unordered_map<coord, int> hash;
+    map<coord, int> hash;
     vector<coord> seq;
     int index;