valgrind: change suppression for libpng

Author: lilith

Diff for: valgrind_suppressions.txt

@@ -157,11 +157,5 @@
    fun:fill_window
    fun:deflate_fast
    fun:deflate
-   fun:png_compress_IDAT
-   fun:png_write_filtered_row
-   fun:png_write_find_filter
-   fun:png_write_row
-   fun:png_write_image
-   fun:png_write_png
    ...
 }