refactor(compiler): remove 'head' tag contains 'html' tag condition code (#5958)

remove 'head' tag contains 'html' tag condition I am not sure this is necessary, but all test passed
after remove the code.

src/compiler/parser/html-parser.js

@@ -222,7 +222,7 @@ export function parseHTML (html, options) {
       }
     }
 
-    const unary = isUnaryTag(tagName) || tagName === 'html' && lastTag === 'head' || !!unarySlash
+    const unary = isUnaryTag(tagName) || !!unarySlash
 
     const l = match.attrs.length
     const attrs = new Array(l)