gitignore: remove useless *~

I changed all the references to 'sed -i~' (which was due to the need for
compatibility between BSD sed on macOS and GNU sed on Linux) to perl,
which is identical on both platforms.

Signed-off-by: Maël Valais <mael@vls.dev>

Author: maelvls

.gitignore

@@ -1,4 +1,3 @@
 ca.crt
 ca.key
 *.t.err
-*~