Fix nontrivial memeset initialization warning in zlib bench tests

GCC complains about initialization of a non-trivial object with memset,
`z_params` is non-trivial because of non-static data member initializer.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

test/bench/zlib/deflate_stream.cpp

@@ -68,7 +68,6 @@ public:
     doDeflateBeast(string_view const& in)
     {
         z_params zs;
-        memset(&zs, 0, sizeof(zs));
         deflate_stream ds;
         ds.reset(
             Z_DEFAULT_COMPRESSION,

test/bench/zlib/inflate_stream.cpp

@@ -102,7 +102,6 @@ public:
     {
         z_params zs;
         std::string out;
-        memset(&zs, 0, sizeof(zs));
         inflate_stream is;
         zs.next_in = &in[0];
         zs.avail_in = in.size();