std::strings: fix join function

std/strings/strings.jule

@@ -459,23 +459,9 @@ pub fn join(parts: []str, sep: str): str {
     | 0:
         ret ""
     | 1:
-        ret parts[1]
+        ret parts[0]
     }
-    let mut n = 0
-    if sep.len > 0 {
-        if sep.len >= int.MAX/(parts.len-1) {
-            panic("std::strings: join: output length overflow")
-        }
-        n += sep.len * (parts.len - 1)
-    }
-    for _, part in parts {
-        if part.len > int.MAX-n {
-            panic("std::strings: join: output length overflow")
-        }
-        n += part.len
-    }
-    let mut s = make(str, n)
-    s += parts[0]
+    let mut s = parts[0]
     for _, part in parts[1:] {
         s += sep
         s += part