Remove attributes section from index.bs

Removed the section on attributes and defined attributes related to matrices.

Author: willow-ahrens

spec/latest/index.bs

@@ -844,22 +844,6 @@ number of logical values in both triangles can be computed in constant time.
 
 </div>
 
-Attributes {#key_attributes}
---------------------------
-The `attributes` key shall denote a dictionary of optional attributes containing
-keys with information about the stored matrix and the data it represents.
-Attributes are optional and may be ignored by a compliant parser.
-
-### Defined Attributes {#defined_attributes}
-
-#### number_of_diagonal_elements #### {#number_of_diagonal_elements_attributes}
-`number_of_diagonal_elements` shall contain an integer value corresponding to
-the number of elements on the stored matrix's diagonal.
-
-Note: implementations are highly encouraged to provide the
-`number_of_diagonal_elements` attribute for matrices with a symmetric,
-skew-symmetric, or Hermitian structure.
-
 Binary Containers {#binary_container}
 =====================================
 Binary containers must store binary arrays in a standardized, cross-platform