Disable doctests

Starting with `random-1.3.0` doctests are executed in a CI by invoking
`doctest` executable directly, which turns out to be the correct way to
use doctest. This was pointed out in #165

In order to avoid `random-1.2.x` major version depending on doctest, this
patch removes doctest usage completely, in favor of a new setup going
forward. However, in order to prevent tooling breakaage downstream that
runs tests we do not remove the `doctest` executable section.

random.cabal

@@ -131,17 +131,7 @@ test-suite doctests
     main-is:          doctests.hs
     hs-source-dirs:   test
     default-language: Haskell2010
-    build-depends:
-        base,
-        doctest >=0.15 && <0.23
-    if impl(ghc >= 8.2) && impl(ghc < 8.10)
-        build-depends:
-            mwc-random >=0.13 && <0.16,
-            primitive >=0.6 && <0.8,
-            random,
-            stm,
-            unliftio >=0.2 && <0.3,
-            vector >= 0.10 && <0.14
+    build-depends:    base
 
 test-suite spec
     type:             exitcode-stdio-1.0

test/doctests.hs

@@ -1,18 +1,4 @@
-{-# LANGUAGE CPP #-}
 module Main where
 
-#if __GLASGOW_HASKELL__ >= 802 && __GLASGOW_HASKELL__ < 810
-
-import Test.DocTest (doctest)
-
-main :: IO ()
-main = doctest ["src"]
-
-#else
-
--- Also disabled in cabal file.
--- TODO: fix doctest support
 main :: IO ()
-main = putStrLn "\nDoctests are not supported for older ghc version\n"
-
-#endif
+main = putStrLn "Doctest have been removed from the cabal into a standalone CI step in random-1.3"