AAPT2: Remove the need for specifying package name in compile phase

The compile phase doesn't use the AndroidManifest, so we had to specify the
package name on the command line.

We can omit the package name, since we don't resolve external references
in the compile phase. Packages that reference the current package will be encoded
with no package name. When loaded by the link phase, the package name will be supplied
and all the references with no package name will use that one.

Change-Id: I9fe4902b747b06899b45c968f30ba1aa05c5cd69