revert embedded templates to use prompt/response

This reverts commit 19753c18c0.

for compat. messages will be added at a later date

template/gemma-instruct.gotmpl

@@ -1,17 +1,5 @@
-{{- if .Messages }}
-{{- range $index, $_ := .Messages }}<start_of_turn>
-{{- if eq .Role "user" }}user
-{{- if and $.System (eq $index 0) }}
-{{ $.System }}
-{{- end }}
-{{- else if eq .Role "assistant" }}model
-{{- end }}
-{{ .Content }}<end_of_turn>
-{{ end }}<start_of_turn>model
-{{ else -}}
 <start_of_turn>user
 {{ if .System }}{{ .System }}
 {{ end }}{{ .Prompt }}<end_of_turn>
 <start_of_turn>model
 {{ .Response }}<end_of_turn>
-{{ end -}}