Fix script for package check to work on macOS

The behaviour of shell parameter expansion on linux and macOS is
different:
- on linux "\/" in the replaced string is interpreted as simply "/"
- on macOS it is interpreted as the full string "\/"
For example, "android.package.example" would be changed to:
- "android/package/example" on linux
- "android\/package\/example" on macOS

The character / is not a special character for pattern matching in bash,
so it doesn't need to be escaped. Hence using / instead of \/ in the
replaced string works on both linux and macOS.

Change-Id: Id6a5cf32afc53d5ffd989c0ac8aa0b9e0fcbaf82
Fixes: 201947033