Remove duplicate test case in mean test

Removed duplicate test case for mean function.

Signed-off-by: Suyash Pathak <[email protected]>

Author: SuYaSh-PaThAk04

lib/node_modules/@stdlib/stats/base/dists/cosine/mean/test/test.js

@@ -57,9 +57,6 @@ tape( 'if provided a nonpositive `s`, the function returns `NaN`', function test
 	y = mean( 2.0, -1.0 );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );
 
-	y = mean( 2.0, -1.0 );
-	t.strictEqual( isnan( y ), true, 'returns expected value' );
-
 	y = mean( 1.0, NINF );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );