[LinearAlgebra] Remove unreliable doctests

The exact textual representation of the output of these doctests depend on the
specific kernel used by the BLAS backend, and can vary between versions of
OpenBLAS (as it did in JuliaLang#41973), or between different CPUs, which makes these
doctests unreliable.

stdlib/LinearAlgebra/src/LinearAlgebra.jl

@@ -385,7 +385,7 @@ control over the factorization of `A`.
  these are already in a factorized form
 
 # Examples
-```jldoctest
+```julia-repl
 julia> A = [1 2.2 4; 3.1 0.2 3; 4 1 2];
 
 julia> X = [1; 2.5; 3];
@@ -426,7 +426,7 @@ control over the factorization of `A`.
  these are already in a factorized form
 
 # Examples
-```jldoctest
+```julia-repl
 julia> A = [1 2.2 4; 3.1 0.2 3; 4 1 2];
 
 julia> X = [1; 2.5; 3];

stdlib/LinearAlgebra/src/hessenberg.jl

@@ -446,7 +446,7 @@ This is useful because multiple shifted solves `(F + μ*I) \\ b`
 Iterating the decomposition produces the factors `F.Q, F.H, F.μ`.
 
 # Examples
-```jldoctest
+```julia-repl
 julia> A = [4. 9. 7.; 4. 4. 1.; 4. 3. 2.]
 3×3 Matrix{Float64}:
  4.0 9.0 7.0