remove docstring

Author: themathqueen

Mathlib/LinearAlgebra/Matrix/PosDef.lean

@@ -22,8 +22,6 @@ of quadratic forms. Most results require `𝕜 = ℝ` or `ℂ`.
 
 ## Main results
 
-* `Matrix.instPartialOrder`: the partial order on matrices
-* `Matrix.instStarOrderedRing`: the star ordered ring instance on matrices
 * `Matrix.posDef_iff_eq_conjTranspose_mul_self`: a matrix `M : Matrix n n 𝕜` is positive
   definite iff it has the form `Bᴴ * B` for some _invertible_ `B`.
 -/