Remove unneeded <algorithm> include in cmath.

It's a remnant from an earlier version of the lerp change
and is unneeded.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@360098 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/cmath b/include/cmath
index f618b1b..0f7018f 100644
--- a/include/cmath
+++ b/include/cmath
@@ -302,7 +302,6 @@
 
 #include <__config>
 #include <math.h>
-#include <algorithm>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)