Remove superfluous std::move calls

Summary: clang-3.7 upstream warns that these calls prevent a copy elision
(-Wpessimizing-move).

Reviewed By: @​mzlee

Differential Revision: D2366951

folly/IPAddress.h

@@ -363,8 +363,8 @@ class IPAddress : boost::totally_ordered<IPAddress> {
    * @return IPAddress instance with bits set to 0
    */
   IPAddress mask(uint8_t numBits) const {
-    return isV4() ? IPAddress(std::move(asV4().mask(numBits)))
-                  : IPAddress(std::move(asV6().mask(numBits)));
+    return isV4() ? IPAddress(asV4().mask(numBits))
+                  : IPAddress(asV6().mask(numBits));
   }
 
   /**

folly/IPAddressV4.h

@@ -180,7 +180,7 @@ class IPAddressV4 : boost::totally_ordered<IPAddressV4> {
   ByteArray4 toByteArray() const {
     ByteArray4 ba{{0}};
     std::memcpy(ba.data(), bytes(), 4);
-    return std::move(ba);
+    return ba;
   }
 
   // @see IPAddress#toFullyQualified