Remove duplicated button in Install web page (go-gitea#27941)

Fix go-gitea#27934 
Regression go-gitea#25648

Author: lng2020

templates/install.tmpl

@@ -325,8 +325,6 @@
 					<!-- Environment Config -->
 					<h4 class="ui dividing header">{{.locale.Tr "install.env_config_keys"}}</h4>
 					<div class="inline field">
-						<label></label>
-						<button class="ui primary button">{{.locale.Tr "install.install_btn_confirm"}}</button>
 						<div class="right-content">
 							{{.locale.Tr "install.env_config_keys_prompt"}}
 						</div>