test: remove duplicate test cases in normal variance

PR-URL: stdlib-js#9826
Closes: stdlib-js#9824

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

Author: GeoDaoyu

lib/node_modules/@stdlib/stats/base/dists/normal/variance/test/test.js

@@ -59,9 +59,6 @@ tape( 'if provided a nonpositive `sigma`, the function returns `NaN`', function
 	y = variance( 2.0, -1.0 );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );
 
-	y = variance( 2.0, -1.0 );
-	t.strictEqual( isnan( y ), true, 'returns expected value' );
-
 	y = variance( 1.0, NINF );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );
 

lib/node_modules/@stdlib/stats/base/dists/normal/variance/test/test.native.js

@@ -68,9 +68,6 @@ tape( 'if provided a nonpositive `sigma`, the function returns `NaN`', opts, fun
 	y = variance( 2.0, -1.0 );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );
 
-	y = variance( 2.0, -1.0 );
-	t.strictEqual( isnan( y ), true, 'returns expected value' );
-
 	y = variance( 1.0, NINF );
 	t.strictEqual( isnan( y ), true, 'returns expected value' );