Remove deprecated jsx-sort-prop-types rule

This has been deprecated for a while. We have decided to remove it
entirely for 6.0.0 (jsx-eslint#686).

Fixes jsx-eslint#549.

Author: lencioni

index.js

@@ -27,7 +27,6 @@ module.exports = {
     'jsx-equals-spacing': require('./lib/rules/jsx-equals-spacing'),
     'jsx-sort-props': require('./lib/rules/jsx-sort-props'),
     'sort-prop-types': require('./lib/rules/sort-prop-types'),
-    'jsx-sort-prop-types': require('./lib/rules/jsx-sort-prop-types'),
     'jsx-boolean-value': require('./lib/rules/jsx-boolean-value'),
     'sort-comp': require('./lib/rules/sort-comp'),
     'require-extension': require('./lib/rules/require-extension'),