GNUmakefile: remove comment outdated after #1435

PR #1435 changed to `cabal run`, dropping previous cabal invocations the comment referred to.
Removing comment, as it is confusing in its present form.

Author: andreasabel

GNUmakefile

@@ -21,10 +21,6 @@ setup: Everything.agda
 
 .PHONY: Everything.agda
 Everything.agda:
-# The command `cabal build` is needed by cabal-install 3.0.0.0 and the
-# command `cabal install` is needed by cabal-install <= 2.4.*. I did
-# not found any problem running both commands with different versions
-# of cabal-install. See Issue #1001.
 	cabal run GenerateEverything
 
 .PHONY: listings