Remove util/cov.sh script

This script hasn't been working and wasn't used for years.

util/cov.sh

@@ -1,37 +0,0 @@
-#!/usr/bin/bash
-
-# This run `kcov` on Clippy. The coverage report will be at
-# `./target/cov/index.html`.
-# `compile-test` is special. `kcov` does not work directly on it so these files
-# are compiled manually.
-
-tests=$(find tests/ -maxdepth 1 -name '*.rs' ! -name compile-test.rs -exec basename {} .rs \;)
-tmpdir=$(mktemp -d)
-
-cargo test --no-run --verbose
-
-for t in $tests; do
-  kcov \
-    --verify \
-    --include-path="$(pwd)/src,$(pwd)/clippy_lints/src" \
-    "$tmpdir/$t" \
-    cargo test --test "$t"
-done
-
-for t in ./tests/compile-fail/*.rs; do
-  kcov \
-    --verify \
-    --include-path="$(pwd)/src,$(pwd)/clippy_lints/src" \
-    "$tmpdir/compile-fail-$(basename "$t")" \
-    cargo run -- -L target/debug -L target/debug/deps -Z no-trans "$t"
-done
-
-for t in ./tests/run-pass/*.rs; do
-  kcov \
-    --verify \
-    --include-path="$(pwd)/src,$(pwd)/clippy_lints/src" \
-    "$tmpdir/run-pass-$(basename "$t")" \
-    cargo run -- -L target/debug -L target/debug/deps -Z no-trans "$t"
-done
-
-kcov --verify --merge target/cov "$tmpdir"/*