ghc-boot[-th]: Drop changelogs

These are internal packages and consequently don't have a changelog

libraries/ghc-boot-th/changelog.md

-## 8.0.1  *May 2016*
-
-  * Bundled with GHC 8.0.1
-
-  * Initial version

libraries/ghc-boot-th/ghc-boot-th.cabal.in

@@ -19,7 +19,6 @@ description:    This library contains various bits shared between the @ghc@ and
                 be depended upon by user code.
 cabal-version:  >=1.10
 build-type:     Simple
-extra-source-files: changelog.md
 
 source-repository head
     type:     git

libraries/ghc-boot/changelog.md

-## 8.0.1  *May 2016*
-
-  * Bundled with GHC 8.0.1
-
-  * Initial version

libraries/ghc-boot/ghc-boot.cabal.in

@@ -24,7 +24,6 @@ description:    This library is shared between GHC, ghc-pkg, and other boot
                 and program do not have to depend on Cabal.
 cabal-version:  >=1.22
 build-type:     Simple
-extra-source-files: changelog.md
 
 source-repository head
     type:     git