Remove unnecessary (and mismatched) mkdtemp declaration.

After https://android-review.googlesource.com/#/c/68700/
we should take out this declaration since it is unnecessary
and mismatched from NDK version.

Change-Id: I3339a173957ff4e72022e1dc4ea80e5111aa5a4a
diff --git a/lib/Support/Unix/Path.inc b/lib/Support/Unix/Path.inc
index e32b474..6a5ebb8c 100644
--- a/lib/Support/Unix/Path.inc
+++ b/lib/Support/Unix/Path.inc
@@ -71,12 +71,6 @@
 # undef HAVE_MKDTEMP
 #endif
 
-// Put in a hack for Android which does not declare the prototype of
-// mkdtemp() in stdlib.h, but with the implementation in libc.so.
-#if defined(__ANDROID__) && defined(HAVE_MKDTEMP)
-extern "C" char *mkdtemp(const char *);
-#endif
-
 namespace {
 inline bool lastIsSlash(const std::string& path) {
   return !path.empty() && path[path.length() - 1] == '/';