bench: remove duplicated require

Signed-off-by: Philipp Burckhardt <pburckhardt@outlook.com>

Author: Planeshifter

lib/node_modules/@stdlib/stats/base/dists/negative-binomial/mean/benchmark/benchmark.native.js

@@ -28,7 +28,6 @@ var isnan = require( '@stdlib/math/base/assert/is-nan' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 var format = require( '@stdlib/string/format' );
 var EPS = require( '@stdlib/constants/float64/eps' );
-var format = require( '@stdlib/string/format' );
 var pkg = require( './../package.json' ).name;