Makefile: do not use --copies when creating git-cola.app
Some python installations (eg. ones created with relocatable-python on macOS)
hit errors when using --copies.
$ make git-cola.app
mkdir -p git-cola.app/Contents/MacOS
mkdir -p git-cola.app/Contents/Resources
python3 -m venv --copies git-cola.app/Contents/Resources
Error: Command '[
'git-cola.app/Contents/Resources/bin/python3', '-Im',
'ensurepip', '--upgrade', '--default-pip'
]' died with <Signals.SIGABRT: 6>.
make: *** [git-cola.app] Error 1
Remove this flag for now.
Signed-off-by: David Aguilar <davvid@gmail.com>