poco: move openssl to propagatedBuildInputs

this is required if someone is using Poco::Crypto, see the following
extract from poco's cmake files:

```cmake
include(CMakeFindDependencyMacro)
find_dependency(PocoFoundation)
find_dependency(OpenSSL REQUIRED COMPONENTS Crypto)
include("${CMAKE_CURRENT_LIST_DIR}/PocoCryptoTargets.cmake")
```

pkgs/development/libraries/poco/default.nix

@@ -31,8 +31,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ cmake pkg-config ];
 
-  buildInputs = [ openssl unixODBC libmysqlclient ];
-  propagatedBuildInputs = [ zlib pcre expat sqlite ];
+  buildInputs = [ unixODBC libmysqlclient ];
+  propagatedBuildInputs = [ zlib pcre expat sqlite openssl ];
 
   outputs = [ "out" "dev" ];