revert embedded templates to use prompt/response

This reverts commit 19753c18c0.

for compat. messages will be added at a later date

template/codellama-70b-instruct.gotmpl

@@ -1,19 +1,10 @@
-{{- if .Messages }}
-{{- if .System }}Source: system
-
- {{ .System }} <step> {{ end }}
-{{- range .Messages }}Source: {{ .Role }}
-
- {{ .Content }} <step> {{ end }}Source: assistant
-Destination: user
-
- {{ else -}}
 {{ if .System }}Source: system
 
  {{ .System }} <step> {{ end }}Source: user
 
  {{ .Prompt }} <step> Source: assistant
+{{- if not .Response }}
 Destination: user
+{{- end }}
 
- {{ .Response }} <step>
-{{- end -}}
+ {{ .Response }} <step>