Following the prior changes, diff is no longer a test suite dependency on
Windows. Closes #2069.
- $PATH is no longer assumed to be "/bin:/usr/bin:/usr/local/bin" if unset
- test suite no longer assumes `python3` exists #2049
- CMake build system locates Python 3 before calling it
-- grep is no longer required to build Graphviz on Windows
+- diff and grep are no longer required to build Graphviz on Windows
### Fixed
find_or_fallback "win_bison win_flex" "$build_utilities_path\winflexbison"
find_or_fallback "makensis" "$build_utilities_path\NSIS\Bin"
find_or_fallback "perl" "$build_utilities_path\Perl64\Bin"
-find_or_fallback "diff" "$build_utilities_path\GnuWin\bin"
find_or_fallback "cmake cpack" "$CMAKE_BIN"
find_or_fallback "msbuild" "$MSBUILD_BIN"