docs: remove unnecessary docker pull from release verification

Docker will automatically pull the image if it isn't found locally.

.github/workflows/release.yaml

@@ -113,7 +113,6 @@ jobs:
             To verify the `lnd` and `lncli` binaries inside the docker images against the signed, reproducible release binaries, there is a verification script in the image that can be called (before starting the container for example):
 
             ```shell
-            $ docker pull lightninglabs/lnd:${{ env.RELEASE_VERSION }}
             $ docker run --rm --entrypoint="" lightninglabs/lnd:${{ env.RELEASE_VERSION }} /verify-install.sh
             $ OK=$?
             $ if [ "$OK" -ne "0" ]; then echo "Verification failed!"; exit 1; done

docs/DOCKER.md

@@ -61,7 +61,6 @@ script in the image that can be called (before starting the container for
 example):
 
 ```shell
-⛰  docker pull lightninglabs/lnd:v0.12.0-beta
 ⛰  docker run --rm --entrypoint="" lightninglabs/lnd:v0.12.0-beta /verify-install.sh
 ⛰  OK=$?
 ⛰  if [ "$OK" -ne "0" ]; then echo "Verification failed!"; exit 1; done

docs/release.md

@@ -99,7 +99,6 @@ script in the image that can be called (before starting the container for
 example):
 
 ```shell
-⛰  docker pull lightninglabs/lnd:v0.12.0-beta
 ⛰  docker run --rm --entrypoint="" lightninglabs/lnd:v0.12.0-beta /verify-install.sh
 ⛰  OK=$?
 ⛰  if [ "$OK" -ne "0" ]; then echo "Verification failed!"; exit 1; done