fix Array#delete

reimplement `Array#delete` in c, fixing `ary.delete(nil, &blk)` firing the block regardless of removal

minimal reproduction:
```rb
ary = [nil]
ret = ary.delete(nil) { "not deleted?" }
```

mrblib/array.rb

@@ -184,21 +184,6 @@ class Array
     end
   end
 
-  ##
-  # call-seq:
-  #   array.delete(obj) -> deleted_object
-  #   array.delete(obj) {|nosuch| ... } -> deleted_object or block_return
-  #
-  # Delete element with index +key+
-  def delete(key, &block)
-    while i = self.index(key)
-      self.delete_at(i)
-      ret = key
-    end
-    return block.call if ret.nil? && block
-    ret
-  end
-
   ##
   # call-seq:
   #   array.sort! -> self

src/array.c

@@ -1397,6 +1397,59 @@ mrb_ary_svalue(mrb_state *mrb, mrb_value ary)
   }
 }
 
+/*
+ * call-seq:
+ *   array.delete(obj) -> deleted_object
+ *   array.delete(obj) {|nosuch| ... } -> deleted_object or block_return
+ *
+ * Delete element with index +key+
+ */
+
+static mrb_value
+mrb_ary_delete(mrb_state *mrb, mrb_value self)
+{
+  struct RArray *ary = RARRAY(self);
+  mrb_value *val_ptr = ARY_PTR(ary);
+  size_t len = ARY_LEN(ary);
+  mrb_bool modified = FALSE;
+
+  mrb_value obj, blk;
+  mrb_get_args(mrb, "o&", &obj, &blk);
+  mrb_value ret = obj;
+
+  size_t i = 0;
+  size_t j = 0;
+  for (; i < len; ++i) {
+    mrb_value elem = val_ptr[i];
+
+    if (mrb_equal(mrb, obj, elem)) {
+      ret = elem;
+      continue;
+    }
+
+    if (i != j) {
+      if (!modified) {
+        ary_modify(mrb, ary);
+        modified = TRUE;
+      }
+      val_ptr[j] = elem;
+    }
+
+    ++j;
+  }
+
+  if (i == j) {
+    if (mrb_proc_p(blk)) {
+      return mrb_yield_argv(mrb, blk, 1, &obj);
+    }
+    return mrb_nil_value();
+  }
+
+  ARY_SET_LEN(ary, j);
+
+  return ret;
+}
+
 void
 mrb_init_array(mrb_state *mrb)
 {
@@ -1414,6 +1467,7 @@ mrb_init_array(mrb_state *mrb)
   mrb_define_method_id(mrb, a, MRB_OPSYM(aset),          mrb_ary_aset,         MRB_ARGS_ARG(2,1)); /* 15.2.12.5.5  */
   mrb_define_method_id(mrb, a, MRB_SYM(clear),           mrb_ary_clear_m,      MRB_ARGS_NONE());   /* 15.2.12.5.6  */
   mrb_define_method_id(mrb, a, MRB_SYM(concat),          mrb_ary_concat_m,     MRB_ARGS_REQ(1));   /* 15.2.12.5.8  */
+  mrb_define_method_id(mrb, a, MRB_SYM(delete),          mrb_ary_delete,       MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, a, MRB_SYM(delete_at),       mrb_ary_delete_at,    MRB_ARGS_REQ(1));   /* 15.2.12.5.9  */
   mrb_define_method_id(mrb, a, MRB_SYM_Q(empty),         mrb_ary_empty_p,      MRB_ARGS_NONE());   /* 15.2.12.5.12 */
   mrb_define_method_id(mrb, a, MRB_SYM(first),           mrb_ary_first,        MRB_ARGS_OPT(1));   /* 15.2.12.5.13 */