Remove title resolver from gatsby theme

packages/gatsby-theme/decks/beep.mdx

@@ -4,3 +4,12 @@
 ---
 
 ## Boop bop
+
+---
+
+Does HMR break with this change?
+
+---
+
+Adding another slide...
+

packages/gatsby-theme/decks/untitled.mdx

@@ -1,6 +0,0 @@
-
-This deck does not have any headings
-
----
-
-Which means the resolver won't get a title

packages/gatsby-theme/gatsby-node.js

@@ -43,12 +43,6 @@ const mdxResolverPassthrough = fieldName => async (
   return result
 }
 
-const resolveTitle = async (...args) => {
-  const headings = await mdxResolverPassthrough('headings')(...args)
-  const [first = {}] = headings
-  return first.value || ''
-}
-
 exports.sourceNodes = ({ actions, schema }) => {
   const { createTypes } = actions
   createTypes(
@@ -59,10 +53,6 @@ exports.sourceNodes = ({ actions, schema }) => {
         slug: {
           type: `String!`,
         },
-        title: {
-          type: `String!`,
-          resolve: resolveTitle,
-        },
         body: {
           type: `String!`,
           resolve: mdxResolverPassthrough(`body`),
@@ -83,7 +73,6 @@ exports.createPages = async ({ graphql, actions, reporter, pathPrefix }) => {
           node {
             id
             slug
-            title
           }
         }
       }

packages/gatsby-theme/src/components/deck.js

@@ -71,7 +71,7 @@ const DefaultMode = ({ children }) => <React.Fragment children={children} />
 
 export default ({
   slides = [],
-  pageContext: { title, slug },
+  pageContext: { slug },
   theme = {},
   themes = [],
   ...props
@@ -112,7 +112,6 @@ export default ({
   return (
     <>
       <Helmet>
-        <title>{title}</title>
         {head}
       </Helmet>
       <GoogleFont theme={mergedTheme} />

packages/gatsby-theme/src/components/decks.js

@@ -31,7 +31,7 @@ export default ({ decks }) => {
                   textDecoration: 'underline',
                 },
               }}>
-              {d.title || d.slug}
+              {d.slug}
             </Link>
           </li>
         ))}