patch 8.1.1035: prop_remove() second argument is not optional

Problem:    prop_remove() second argument is not optional.
Solution:   Fix argument count.  Use "buf" instead of "curbuf". (closes #4147)
diff --git a/src/textprop.c b/src/textprop.c
index 674faeb..34738ad 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -629,7 +629,10 @@
 			mch_memmove(newptr, buf->b_ml.ml_line_ptr,
 							buf->b_ml.ml_line_len);
 			buf->b_ml.ml_line_ptr = newptr;
-			curbuf->b_ml.ml_flags |= ML_LINE_DIRTY;
+			buf->b_ml.ml_flags |= ML_LINE_DIRTY;
+
+			cur_prop = buf->b_ml.ml_line_ptr + len
+							+ idx * sizeof(textprop_T);
 		    }
 
 		    taillen = buf->b_ml.ml_line_len - len