This change removes redundant strict comparisons flagged by PHPStan and simplifies the affected conditions.

[arshidkv12]

• WP_Links_List_Table: Check $cat_id against 0 instead of comparing it with the string 'all'.
• wp_get_layout_style(): Check for an empty string after trim() instead of checking against null.
• WP_Rewrite: Simplify array_search() result checks by testing only against false; array_search() does not return null.
• PHPStan baseline: Remove the corresponding notIdentical.alwaysTrue suppressions that are no longer needed.

This is a cleanup-only change with no intended behavioral change.