[opinionated] Remove custom css_before_spread_props lint rule

- As noted, Emotion does not auto-merge non-top-level props so we need to do it manually for css merging to work correctly.

This means a lot of disables - we're probably better off linting for the presence of `shouldRenderCustomStyles` instead, which actually tests for working Emotion CSS

.eslintplugin.js

@@ -4,6 +4,5 @@ exports.rules = {
   'require-license-header': require('./scripts/eslint-plugin/require_license_header'),
   'forward-ref': require('./scripts/eslint-plugin/forward_ref_display_name'),
   'css-logical-properties': require('./scripts/eslint-plugin/css_logical_properties'),
-  css_before_spread_props: require('./scripts/eslint-plugin/css_before_spread_props'),
   'require-cypress-references': require('./scripts/eslint-plugin/require_cypress_references'),
 };

.eslintrc.js

@@ -77,7 +77,6 @@ module.exports = {
     'local/href-with-rel': 'error',
     'local/forward-ref': 'error',
     'local/css-logical-properties': 'error',
-    'local/css_before_spread_props': 'error',
     'local/require-cypress-references': 'error',
     'local/require-license-header': [
       'warn',

src/components/page/page_section/page_section.tsx

@@ -100,14 +100,11 @@ export const EuiPageSection: FunctionComponent<EuiPageSectionProps> = ({
     bottomBorder === true && styles.border,
     alignment.toLowerCase().includes('center') && contentStyles.center,
     restrictWidth && contentStyles.restrictWidth,
-    contentProps?.css && contentProps.css,
+    contentProps?.css,
   ];
 
   return (
     <Component css={cssStyles} {...rest}>
-      {/* `css` must be merged manually after props spread on the content wrapper -
-      Emotion does not automatically correctly merge `css` on non-component JSX */}
-      {/* eslint-disable-next-line local/css_before_spread_props */}
       <div {...contentProps} css={cssContentStyles} style={widthStyles}>
         {children}
       </div>