Exclude package installer during secure FRP

When Secure FRP is enabled, any application with INSTALL_PACKAGES is
allowed to install APKs. However, we exclude the package installer
since it installs packages on behalf of other applications thus
allowing packages to be installed by any application [eg. chrome] on
the device.

Bug: 141262900
Test: atest CtsSecureFrpInstallTestCases
Test: atest CtsPackageInstallTestCases
Change-Id: I73e23f9e264dfbafc0bd7c81301f6a86b1e2c8f7