nixos/testing: remove remaining coverage-data logic

This isn't used anymore as per
https://github.com/NixOS/nixpkgs/pull/72354#discussion_r451031449.

pkgs/build-support/release/default.nix

@@ -41,10 +41,6 @@ rec {
       doCoverityAnalysis = true;
     } // args);
 
-  gcovReport = args: import ./gcov-report.nix (
-    { inherit runCommand lcov rsync;
-    } // args);
-
   rpmBuild = args: import ./rpm-build.nix (
     { inherit vmTools;
     } // args);

pkgs/build-support/release/gcov-report.nix

@@ -1,49 +0,0 @@
-{ runCommand, lcov, rsync, coverageRuns, lcovFilter ? [ "/nix/store/*" ], baseDirHack ? false }:
-
-runCommand "coverage"
-  { buildInputs = [ lcov rsync ];
-    inherit lcovFilter baseDirHack;
-  }
-  ''
-    mkdir -p $TMPDIR/gcov $out/nix-support $out/coverage
-    info=$out/coverage/full.info
-
-    for p in ${toString coverageRuns}; do
-        if [ -f $p/nix-support/hydra-build-products ]; then
-            cat $p/nix-support/hydra-build-products >> $out/nix-support/hydra-build-products
-        fi
-
-        [ ! -e $p/nix-support/failed ] || touch $out/nix-support/failed
-
-        opts=
-        for d in $p/coverage-data/*; do
-            for i in $(cd $d/nix/store && ls); do
-                if ! [ -e /nix/store/$i/.build ]; then continue; fi
-                if [ -e $TMPDIR/gcov/nix/store/$i ]; then continue; fi
-                echo "copying $i..."
-                rsync -a /nix/store/$i/.build/* $TMPDIR/gcov/
-                if [ -n "$baseDirHack" ]; then
-                    opts="-b $TMPDIR/gcov/$(cd /nix/store/$i/.build && ls)"
-                fi
-            done
-
-            for i in $(cd $d/nix/store && ls); do
-                rsync -a $d/nix/store/$i/.build/* $TMPDIR/gcov/ --include '*/' --include '*.gcda' --exclude '*'
-            done
-        done
-
-        chmod -R u+w $TMPDIR/gcov
-
-        echo "producing info..."
-        geninfo --ignore-errors source,gcov $TMPDIR/gcov --output-file $TMPDIR/app.info $opts
-        cat $TMPDIR/app.info >> $info
-    done
-
-    echo "making report..."
-    set -o noglob
-    lcov --remove $info ''$lcovFilter > $info.tmp
-    set +o noglob
-    mv $info.tmp $info
-    genhtml --show-details $info -o $out/coverage
-    echo "report coverage $out/coverage" >> $out/nix-support/hydra-build-products
-  ''