Remove unused api-debug (#722)

**What this PR does / why we need it**:

**Which issue(s) this PR fixes**:

Fixes #

**Does this PR introduce a user-facing change?**:
<!--
If no, just write "NONE" in the release-note block below.
-->
```release-note
NONE
```

/cc @nakabonne 
This PR was merged by Kapetanios.

cmd/image.bzl

@@ -1,7 +1,6 @@
 def all_images():
     cmds = {
         "api": "api",
-        "api-debug": "api-debug",
         "piped": "piped",
         "web": "web",
         "helloworld": "helloworld",

manifests/pipecd/templates/deployment.yaml

@@ -87,11 +87,7 @@ spec:
     spec:
       containers:
         - name: api
-{{- if .Values.api.useDebugImage }}
-          image: "gcr.io/pipecd/api-debug:{{ .Values.api.imageTag | default .Chart.AppVersion }}"
-{{- else }}
           image: "gcr.io/pipecd/api:{{ .Values.api.imageTag | default .Chart.AppVersion }}"
-{{- end }}
           imagePullPolicy: IfNotPresent
           args:
           - server

manifests/pipecd/values.yaml

@@ -34,7 +34,6 @@ gateway:
 api:
   replicasCount: 1
   imageTag: ""
-  useDebugImage: true
   args:
     cacheAddress: ""
     useFakeResponse: false