Http: drop the redundant boost::filesystem alias in CurlGlobalInit (#16446)

The constructor re-declares `namespace fs = boost::filesystem;`, shadowing the
identical file-scope alias the rest of the file already uses. Removing it
leaves every `fs::` in the file resolving to that one declaration.

No functional change.

src/slic3r/Utils/Http.cpp

@@ -61,7 +61,6 @@ struct CurlGlobalInit
             "/etc/ssl/ca-bundle.pem"              // OpenSUSE Tumbleweed
         };
 
-        namespace fs = boost::filesystem;
         // Env var name for the OpenSSL CA bundle (SSL_CERT_FILE nomally)
         const char *const SSL_CA_FILE = X509_get_default_cert_file_env();
         const char * ssl_cafile = ::getenv(SSL_CA_FILE);