httpclient: 清理 ssrf.go S1017 lint 警告

matchAllowedHost 里两处 if strings.HasPrefix(...) pattern = pattern[N:]
替成无条件 strings.TrimPrefix, 行为完全等价 (前缀不匹配时 TrimPrefix
是 no-op). 触发 S1017 (Should replace this if statement with an
unconditional strings.TrimPrefix).

净 -4 行, 函数语义不变, matchAllowedHost 现有测试 (ssrf_test.go)
覆盖的精确/后缀/wildcard 三种 host 匹配路径都不变.

Co-Authored-By: Claude <noreply@anthropic.com>

internal/httpclient/ssrf.go

@@ -116,12 +116,8 @@ func matchAllowedHost(host, pattern string) bool {
 		return true
 	}
 
-	if strings.HasPrefix(pattern, "*.") {
-		pattern = pattern[2:]
-	}
-	if strings.HasPrefix(pattern, ".") {
-		pattern = pattern[1:]
-	}
+	pattern = strings.TrimPrefix(pattern, "*.")
+	pattern = strings.TrimPrefix(pattern, ".")
 
 	return host == pattern || strings.HasSuffix(host, "."+pattern)
 }