revert embedded templates to use prompt/response

This reverts commit 19753c18c0.

for compat. messages will be added at a later date

template/mistral-instruct.gotmpl

@@ -1,10 +1,3 @@
-{{- if .Messages }}
-{{- range $index, $_ := .Messages }}
-{{- if eq .Role "user" }}[INST] {{ if and $.System (eq (len (slice $.Messages $index)) 1) }}{{ $.System }}
-{{ end }}{{ .Content }}
-{{- else if eq .Role "assistant" }}[/INST] {{ .Content }}</s>
-{{- end }}
-{{- end }}[/INST]
-{{- else -}}
-[INST] {{ if .System }}{{ .System }} {{ end }}{{ .Prompt }}[/INST] {{ .Response }}</s>
-{{- end -}}
+[INST] {{ if .System }}{{ .System }}
+
+{{ end }}{{ .Prompt }}[/INST] {{ .Response }}</s>