perltidy: Don't write backup files

Newer perltidy versions can just avoid writing backup files, so we don't
need the old dance of deleting them afterwards.  Supported since 20120619.

https://metacpan.org/source/SHANCOCK/Perl-Tidy-20120619/CHANGES#L61

src/tools/pgindent/perltidyrc

 --add-whitespace
 --backup-and-modify-in-place
+--backup-file-extension=/
 --delete-old-whitespace
 --entab-leading-whitespace=4
 --keep-old-blank-lines=2

src/tools/pgindent/pgperltidy

@@ -18,6 +18,3 @@ PERLTIDY=${PERLTIDY:-perltidy}
 ) |
 sort -u |
 xargs $PERLTIDY --profile=src/tools/pgindent/perltidyrc
-
-# perltidyrc specifies --backup-and-modify-in-place, so get rid of .bak files
-find . -type f -name '*.bak' | xargs rm