Remove disabled from text inputs in form editor

Was causing that those inputs were rendered with transparent background
[MAILPOET-2609]

assets/js/src/form_editor/blocks/custom_text/edit.jsx

@@ -86,7 +86,6 @@ const CustomTextEdit = ({ attributes, setAttributes, clientId }) => {
       className="mailpoet_text"
       type="text"
       name="custom_text"
-      disabled
       placeholder={placeholder}
       data-automation-id="editor_custom_text_input"
     />

assets/js/src/form_editor/blocks/email/edit.jsx

@@ -39,7 +39,6 @@ const EmailEdit = ({ attributes, setAttributes }) => {
       className="mailpoet_text"
       type="email"
       name="email"
-      disabled
       placeholder={placeholder}
       data-automation-id="editor_email_input"
     />

assets/js/src/form_editor/blocks/first_name/edit.jsx

@@ -45,7 +45,6 @@ const FirstNameEdit = ({ attributes, setAttributes }) => {
       className="mailpoet_text"
       type="text"
       name="first_name"
-      disabled
       placeholder={placeholder}
       data-automation-id="editor_first_name_input"
     />

assets/js/src/form_editor/blocks/last_name/edit.jsx

@@ -45,7 +45,6 @@ const LastNameEdit = ({ attributes, setAttributes }) => {
       className="mailpoet_text"
       type="text"
       name="last_name"
-      disabled
       placeholder={placeholder}
       data-automation-id="editor_last_name_input"
     />