docs(specs): remove root level state machine modules (celestiaorg#3275)

Closes celestiaorg#3270 by
removing the redundant list of state machine modules on the root level
README.md.
Closes celestiaorg#3151 by git
ignoring `theme`.

specs/.gitignore

@@ -1 +1,2 @@
 book
+theme

specs/book.toml

@@ -2,7 +2,6 @@
 authors = ["Celestia Labs"]
 language = "en"
 multilingual = false
-src = "src"
 title = "Celestia App Specifications"
 
 [output.html]

specs/src/README.md

@@ -16,10 +16,4 @@
   - [Resource Pricing](./specs/resource_pricing.md)
   - [Multisig](./specs/multisig.md)
 - [State Machine Modules](./specs/state_machine_modules.md)
-  - [blob](https://github.com/celestiaorg/celestia-app/blob/main/x/blob/README.md)
-  - [blobstream](https://github.com/celestiaorg/celestia-app/blob/main/x/blobstream/README.md)
-  - [mint](https://github.com/celestiaorg/celestia-app/blob/main/x/mint/README.md)
-  - [paramfilter](https://github.com/celestiaorg/celestia-app/blob/main/x/paramfilter/README.md)
-  - [upgrade](https://github.com/celestiaorg/celestia-app/blob/main/x/upgrade/README.md)
-  - [tokenfilter](https://github.com/celestiaorg/celestia-app/blob/main/x/tokenfilter/README.md)
 - [Mainnet Parameters](./specs/params.md)