Remove unused strings.h #include from crypto/mem.c

crypto/mem.c #include's <strings.h>, but doesn't use call any functions
from it.

Change-Id: If60b31be7dd6b347bcb077a59825a557a2492081
Reviewed-on: https://boringssl-review.googlesource.com/25964
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/mem.c b/crypto/mem.c
index 67f74b7..50c6fe6 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -65,8 +65,6 @@
 OPENSSL_MSVC_PRAGMA(warning(push, 3))
 #include <windows.h>
 OPENSSL_MSVC_PRAGMA(warning(pop))
-#else
-#include <strings.h>
 #endif
 
 #include "internal.h"