Allow for single-line deletions in clang_tidy.py (#19082)

Allow for single-line deletions in clang_tidy.py (#19082)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19082

When you have just one line of deletions, just as with additions, there is no count printed.
Without this fix, we ignore all globs with single-line deletions when selecting which lines were changed.
When all the changes in the file were single-line, this meant no line-filtering at all!

Differential Revision: D14860426

fbshipit-source-id: c60e9d84f9520871fc0c08fa8c772c227d06fa27