Make cabal sdist work for crucible-cli{,-llvm}

* Neither package's `.cabal` file contains a `README.md` file, so remove
  mention of this file name from the `extra-doc-files`.

* `crucible-cli.cabal` uses double-star syntax (`test-data/**/*.cbl`) in its
  `extra-source-files`, which requires a `cabal-version` or `2.4` or greater.
  Make sure that `crucible-cli.cabal` properly declares this version
  dependency.

Fixes #1209.

crucible-cli/crucible-cli.cabal

@@ -1,4 +1,4 @@
-Cabal-version: 2.2
+Cabal-version: 2.4
 Name:          crucible-cli
 Version:       0.1
 Author:        Galois Inc.
@@ -10,7 +10,7 @@ Category:      Language
 Synopsis:      A library for sharing code between Crucible CLI frontends
 -- Description:
 
-extra-doc-files: CHANGELOG.md, README.md
+extra-doc-files: CHANGELOG.md
 extra-source-files:
   test-data/**/*.cbl
   test-data/**/*.out.good

crucible-llvm-cli/crucible-llvm-cli.cabal

@@ -10,7 +10,7 @@ Category:      Language
 Synopsis:      A Crucible CLI frontend for the LLVM language extension
 -- Description:
 
-extra-doc-files: CHANGELOG.md, README.md
+extra-doc-files: CHANGELOG.md
 extra-source-files:
   test-data/*.cbl
   test-data/*.out.good