[docs] change docstring to match code (#55013)
The docstring of `LinearAlgebra.reflectorApply!` is incorrect. It says
the function is applying `(I - τ*[1; x] * [1; x]')*A`, but in reality it
is applying `(I - conj(τ)*[1; x[2:end]]*[1; x[2:end]]')*A`. You can
check that by looking at the code, or running for example
```julia
using LinearAlgebra
T=ComplexF64;d=5;
τ=randn(T);x=randn(T,d);A=randn(T,d,d);
(I - conj(τ)*[1; x[2:end]]*[1; x[2:end]]')*A
LinearAlgebra.reflectorApply!(x,τ,A)
```
