Refactor to remove unused import.

recipes/libpng/all/conanfile.py

@@ -2,7 +2,7 @@
 from conan.errors import ConanInvalidConfiguration
 from conan.tools.apple import is_apple_os
 from conan.tools.cmake import CMake, CMakeToolchain, CMakeDeps, cmake_layout
-from conan.tools.files import apply_conandata_patches, copy, export_conandata_patches, get, replace_in_file, rm, rmdir
+from conan.tools.files import apply_conandata_patches, copy, export_conandata_patches, get, rm, rmdir
 from conan.tools.microsoft import is_msvc
 from conan.tools.scm import Version
 import os