Remove dependent issues trigger (#2815)

Essentially, on #2814 I noticed that saying `#2811 depends` [word break] `on #2813` led to this trigger activating. This led to me asking whether anyone uses it, and responses were okay with it being removed. It's had [limited use](https://github.com/carbon-language/carbon-lang/pulls?q=is%3Apr+%22By+Dependent+Issues%22+), so this shouldn't be expected to affect workflows (unfortunately partly because dependent PRs aren't handled well by GitHub's review interface).

Discussed [on Discord](https://discord.com/channels/655572317891461132/707150492370862090/1103721071221407835).

Also minor edit to replace `-` with `_` in pre-commit filename ([style](https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/cpp_style_guide.md#file-names)).

.github/workflows/dependent-issues.yaml

@@ -1,32 +0,0 @@
-# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-# Exceptions. See /LICENSE for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-name: Dependent Issues
-
-on:
-  issues:
-    types:
-      - opened
-      - edited
-      - reopened
-  pull_request_target:
-    types:
-      - opened
-      - edited
-      - reopened
-      - synchronize
-  schedule:
-    - cron: '0 0 * * *' # daily
-
-jobs:
-  check:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: z0al/dependent-issues@v1
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        with:
-          label: dependent
-          check_issues: on
-          keywords: depends on, blocked by