Generate plugin snap configs as needed (#8411)

While reviewing https://github.com/certbot/certbot/pull/8404, it occurred to me that we're keeping both the generated files and the script used to generate them in `git`. Keeping both around seems unnecessary and is almost asking for the files to get out of sync at some point in the future. I fixed that by removing the files, adding them to `.gitignore`, and updating `build_remote.py` to generate them as needed.

* Remove generated files.

* Add generated files to gitignore.

* Reuse generate_dnsplugins_all.sh in build_remote

certbot-dns-google/snap/hooks/post-refresh

@@ -1,21 +0,0 @@
-#!/bin/sh -e
-# This file is generated automatically and should not be edited manually.
-
-# get certbot version
-if [ ! -f "$SNAP/certbot-shared/certbot-version.txt" ]; then
-  echo "No certbot version available; not doing version comparison check" >> "$SNAP_DATA/debuglog"
-  exit 0
-fi
-cb_installed=$(cat $SNAP/certbot-shared/certbot-version.txt)
-
-# get required certbot version for plugin. certbot version must be at least the plugin's
-# version. note that this is not the required version in setup.py, but the version number itself.
-cb_required=$(grep -oP "version = '\K.*(?=')" $SNAP/setup.py)
-
-
-$SNAP/bin/python3 -c "import sys; from packaging import version; sys.exit(1) if  version.parse('$cb_installed') < version.parse('$cb_required') else sys.exit(0)" || exit_code=$?
-if [ "$exit_code" -eq 1 ]; then
-  echo "Certbot is version $cb_installed but needs to be at least $cb_required before" \
-    "this plugin can be updated; will try again on next refresh."
-  exit 1
-fi

certbot-dns-google/snap/snapcraft.yaml

@@ -1,41 +0,0 @@
-# This file is generated automatically and should not be edited manually.
-name: certbot-dns-google
-summary: Google Cloud DNS Authenticator plugin for Certbot
-description: Google Cloud DNS Authenticator plugin for Certbot
-confinement: strict
-grade: stable
-base: core20
-adopt-info: certbot-dns-google
-
-parts:
-  certbot-dns-google:
-    plugin: python
-    source: .
-    constraints: [$SNAPCRAFT_PART_SRC/snap-constraints.txt]
-    override-pull: |
-        snapcraftctl pull
-        snapcraftctl set-version `grep ^version $SNAPCRAFT_PART_SRC/setup.py | cut -f2 -d= | tr -d "'[:space:]"`
-    build-environment:
-      - SNAP_BUILD: "True"
-    # To build cryptography and cffi if needed
-    build-packages: [gcc, libffi-dev, libssl-dev, python3-dev]
-  certbot-metadata:
-    plugin: dump
-    source: .
-    stage: [setup.py, certbot-shared]
-    override-pull: |
-        snapcraftctl pull
-        mkdir -p $SNAPCRAFT_PART_SRC/certbot-shared
-
-slots:
-  certbot:
-    interface: content
-    content: certbot-1
-    read:
-      - $SNAP/lib/python3.8/site-packages
-
-plugs:
-  certbot-metadata:
-    interface: content
-    content: metadata-1
-    target: $SNAP/certbot-shared