fix: release scripts from issuing overlapping phases

`mvn deploy` will run `mvn install` so specifying `mvn install deploy` is redundant at best. At worst, it will cause plugins like maven-shade-plugin to be executed twice re-shading itself

Source-Author: Igor Bernstein <igorbernstein@google.com>
Source-Date: Wed Apr 14 13:16:03 2021 -0400
Source-Repo: googleapis/synthtool
Source-Sha: 8285c2b4cdbc3771d031ad91e1c4ec9e55fff45d
Source-Link: googleapis/synthtool@8285c2b

.kokoro/release/snapshot.sh

@@ -25,7 +25,7 @@ grep SNAPSHOT versions.txt
 setup_environment_secrets
 create_settings_xml_file "settings.xml"
 
-mvn clean install deploy -B \
+mvn clean deploy -B \
   --settings ${MAVEN_SETTINGS_FILE} \
   -DperformRelease=true \
   -Dgpg.executable=gpg \

.kokoro/release/stage.sh

@@ -29,7 +29,7 @@ create_settings_xml_file "settings.xml"
 
 # attempt to stage 3 times with exponential backoff (starting with 10 seconds)
 retry_with_backoff 3 10 \
-  mvn clean install deploy -B \
+  mvn clean deploy -B \
     --settings ${MAVEN_SETTINGS_FILE} \
     -DskipTests=true \
     -DperformRelease=true \

synth.metadata

@@ -11,7 +11,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "082e1ca0863b13ada8594fe91845380765da5b70"
+        "sha": "8285c2b4cdbc3771d031ad91e1c4ec9e55fff45d"
       }
     }
   ],