Revert "Use cstdint types in integral_types.h"

This reverts commit 101ae83.

This unbreaks pywraps2_test in Travis CI's configuration.
https://travis-ci.org/google/s2geometry/jobs/460894006

======================================================================
ERROR: testS2CellDistance (__main__.PyWrapS2TestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/google/s2geometry/src/python/pywraps2_test.py", line 213, in testS2CellDistance
    cell = s2.S2Cell(s2.S2CellId(0x1000000000000000))
  File "/home/travis/build/google/s2geometry/build/python/pywraps2.py", line 311, in __init__
    this = _pywraps2.new_S2CellId(*args)
NotImplementedError: Wrong number or type of arguments for overloaded function 'new_S2CellId'.
  Possible C/C++ prototypes are:
    S2CellId::S2CellId(uint64)
    S2CellId::S2CellId(S2Point const &)
    S2CellId::S2CellId(S2LatLng const &)
    S2CellId::S2CellId()

Possibly related to different SWIG or stdint.i versions.  It looks like
the uint64 -> uint64_t mapping is not being found.

It worked when I tested.

src/python/s2.i

@@ -1,12 +1,15 @@
 %include "std_vector.i"
 %include "std_string.i"
-%include "stdint.i"
 
+%template() std::vector<unsigned long long>;
 %template() std::vector<S2CellId>;
 %template() std::vector<S2Point>;
 %template() std::vector<S2LatLng>;
 
+%apply int {int32};
+%apply unsigned long long {uint64};
 %apply std::string {string};
+%apply std::vector<unsigned long long> const & {std::vector<uint64> const &};
 
 // Standard Google convention is to ignore all functions and methods, and
 // selectively add back those for which wrapping is both required and

src/s2/base/integral_types.h

@@ -16,22 +16,16 @@
 #ifndef S2_BASE_INTEGRAL_TYPES_H_
 #define S2_BASE_INTEGRAL_TYPES_H_
 
-#include <cstdint>
-#include <type_traits>
+using int8 = signed char;
+using int16 = short;
+using int32 = int;
+using int64 = long long;
 
-using int8 = int8_t;
-using int16 = int16_t;
-using int32 = int32_t;
-using int64 = int64_t;
+using uint8 = unsigned char;
+using uint16 = unsigned short;
+using uint32 = unsigned int;
+using uint64 = unsigned long long;
 
-using uint8 = uint8_t;
-using uint16 = uint16_t;
-using uint32 = uint32_t;
-using uint64 = uint64_t;
-
-static_assert(sizeof(void *) == 8 || sizeof(void *) == 4,
-              "void * must be 32 or 64 bits.");
-using uword_t =
-    std::conditional<sizeof(void *) == 8, uint64_t, uint32_t>::type;
+using uword_t = unsigned long;
 
 #endif  // S2_BASE_INTEGRAL_TYPES_H_