Remove explicit test for helper function

Author: jishnub

test/tridiag.jl

@@ -1155,10 +1155,6 @@ end
 
 @testset "SymTridiagonal from Symmetric" begin
     S = Symmetric(reshape(1:9, 3, 3))
-    @testset "helper functions" begin
-        @test LinearAlgebra._issymmetric(S)
-        @test !LinearAlgebra._issymmetric(Array(S))
-    end
     ST = SymTridiagonal(S)
     @test ST == SymTridiagonal(diag(S), diag(S,1))
     S = Symmetric(Tridiagonal(1:3, 1:4, 1:3))