page_zip_reorganize(): Restore the page on failure.
In callers, omit now-redundant calls to page_zip_decompress().

btr_page_reorganize_low(): Define in static scope only, and
remove the z_level parameter. Assert that ROW_FORMAT is not COMPRESSED.

btr_page_reorganize_block(), btr_page_reorganize(): Invoke
page_zip_reorganize() for ROW_FORMAT=COMPRESSED.