Remove unused matrix type params in diag methods (JuliaLang#56048)

These parameters are not used in the method, and are unnecessary for
dispatch.

Author: jishnub

stdlib/LinearAlgebra/src/bidiag.jl

@@ -377,7 +377,7 @@ function triu!(M::Bidiagonal{T}, k::Integer=0) where T
     return M
 end
 
-function diag(M::Bidiagonal{T}, n::Integer=0) where T
+function diag(M::Bidiagonal, n::Integer=0)
     # every branch call similar(..., ::Int) to make sure the
     # same vector type is returned independent of n
     if n == 0

stdlib/LinearAlgebra/src/diagonal.jl

@@ -708,7 +708,7 @@ adjoint(D::Diagonal) = Diagonal(adjoint.(D.diag))
 permutedims(D::Diagonal) = D
 permutedims(D::Diagonal, perm) = (Base.checkdims_perm(D, D, perm); D)
 
-function diag(D::Diagonal{T}, k::Integer=0) where T
+function diag(D::Diagonal, k::Integer=0)
     # every branch call similar(..., ::Int) to make sure the
     # same vector type is returned independent of k
     if k == 0

stdlib/LinearAlgebra/src/tridiag.jl

@@ -609,7 +609,7 @@ issymmetric(S::Tridiagonal) = all(issymmetric, S.d) && all(Iterators.map((x, y)
 
 \(A::Adjoint{<:Any,<:Tridiagonal}, B::Adjoint{<:Any,<:AbstractVecOrMat}) = copy(A) \ B
 
-function diag(M::Tridiagonal{T}, n::Integer=0) where T
+function diag(M::Tridiagonal, n::Integer=0)
     # every branch call similar(..., ::Int) to make sure the
     # same vector type is returned independent of n
     if n == 0