fix(checkbox): use camelCase and remove id

Author: thetaPC

static/usage/v8/checkbox/helper-error/angular/example_component_html.md

@@ -1,6 +1,6 @@
 ```html
 <form [formGroup]="myForm" (ngSubmit)="onSubmit()">
-  <ion-checkbox formControlName="agree" helper-text="This needs to be checked" error-text="This field is required">
+  <ion-checkbox formControlName="agree" helperText="This needs to be checked" errorText="This field is required">
     I agree to the terms and conditions
   </ion-checkbox>
 

static/usage/v8/checkbox/helper-error/vue.md

@@ -1,6 +1,6 @@
 ```html
 <template>
-  <form id="my-form" @submit.prevent="submit">
+  <form @submit.prevent="submit">
     <ion-checkbox
       v-model="agree"
       helper-text="This needs to be checked"