glsl: Remove stale lower_instructions comments.

Should have been in 3a42e92a4f ("glsl: Drop the dead MOD_TO_FLOOR path.")

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16823>

src/compiler/glsl/lower_instructions.cpp

@@ -72,13 +72,6 @@
  * do have base 2 versions, so this pass converts exp and log to exp2
  * and log2 operations.
  *
- * Many GPUs don't have a MOD instruction (945 and 965 included), and
- * if we have to break it down like this anyway, it gives an
- * opportunity to do things like constant fold the (1.0 / op1) easily.
- *
- * Note: before we used to implement this as op1 * fract(op / op1) but this
- * implementation had significant precision errors.
- *
  * LDEXP_TO_ARITH:
  * -------------
  * Converts ir_binop_ldexp to arithmetic and bit operations for float sources.