Remove some old docs that are no longer relevant (#278)

Author: chenglou

_blogposts/archive/bucklescript-release-3-0-0.mdx

@@ -1,10 +1,10 @@
 ---
 author: hongbo
-date: "2018-04-16" 
+date: "2018-04-16"
 previewImg:
 category: compiler
 badge: release
-title: Announcing BuckleScript 3.0 
+title: Announcing BuckleScript 3.0
 description: |
 ---
 
@@ -19,8 +19,7 @@ description: |
   This caused quite a bit of confusion for newcomers. It now compiles to JS
   `true`/`false`. Special thanks to [Cristiano](https://twitter.com/ccrisccris)
   for all the hard work.
-- New [object type
-  feature](/docs/reason-compiler/latest/object#abstract-record-mode). This is
+- New `[bs.deriving abstract`] feature. This is
   an experimental and potentially much better way to bind to JS objects that
   potentially obsoletes the need for a few other APIs. Please see the linked
   docs and help us test it!

_blogposts/archive/state-of-reasonml-org-2020-q2-pt1.mdx

@@ -73,7 +73,7 @@ Our goal is to have a properly curated, well structured and streamlined overview
 
 <Image withShadow={true} src="https://res.cloudinary.com/dmm9n7v9f/image/upload/v1588605830/Reason%20Association/reasonml.org/reasonml-org-structure-retina_rjhvta.jpg" caption="First hand-sketches of the reasonml.org structure"/>
 
-It didn't take long until we realized that we can't just keep the upstream version in its original form, so we started to make adaptations where it made sense. We also accepted new additions from the community, such as explanations about [function signatures on optional arguments](/docs/manual/latest/function#signatures-and-type-annotations) in the Reason manual, or a new [decorator overview](/docs/reason-compiler/latest/decorators) in the BuckleScript section.
+It didn't take long until we realized that we can't just keep the upstream version in its original form, so we started to make adaptations where it made sense. We also accepted new additions from the community, such as explanations about [function signatures on optional arguments](/docs/manual/latest/function#signatures-and-type-annotations) in the Reason manual, or a new decorator overview in the BuckleScript section.
 
 
 That said, we do keep track of new changes on the upstream sources and cherry-pick changes if necessary. To make this process more transparent, we introduced a version table on our [startpage](/) to make it easier to see the latest cherry-pick commit for each resource (ReasonML, BuckleScript, etc.).