revert embedded templates to use prompt/response

This reverts commit 19753c18.

for compat. messages will be added at a later date

template/testdata/mistral-instruct.gotmpl/system-user-assistant-user

-[INST] Hello, how are you?[/INST] I'm doing great. How can I help you today?</s>[INST] You are a helpful assistant.
-I'd like to show off how chat templating works![/INST]
+[INST] You are a helpful assistant.
+
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+Hello, how are you?[/INST] I'm doing great. How can I help you today?</s>[INST] I'd like to show off how chat templating works![/INST]
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template/vicuna.gotmpl

-{{- if .Messages }}
-{{- if .System }}{{ .System }}
-
-{{ end }}
-{{- range .Messages }}
-{{- if eq .Role "user" }}USER: {{ .Content }}
-{{ else if eq .Role "assistant" }}ASSISTANT: {{ .Content }}</s>
-{{ end }}
-{{- end }}ASSISTANT:
-{{- else -}}
 {{ if .System }}{{ .System }}
 
 {{ end }}{{ if .Prompt }}USER: {{ .Prompt }}
 {{ end }}ASSISTANT: {{ .Response }}</s>
-{{ end -}}
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template/zephyr.gotmpl

-{{- if .Messages }}
-{{- if .System }}<|system|>
-{{ .System }}</s>
-{{ end }}
-{{- range .Messages }}<|{{ .Role }}|>
-{{ .Content }}</s>
-{{ end }}<|assistant|>
-{{ else -}}
 {{ if .System }}<|system|>
 {{ .System }}</s>
 {{ end }}{{ if .Prompt }}<|user|>
 {{ .Prompt }}</s>
 {{ end }}<|assistant|>
 {{ .Response }}</s>
-{{ end -}}
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