Don't build hiddenapi flags or encode dex for unbundled builds

Builds with TARGET_BUILD_APPS shouldn't build the hiddenapi flags
or encode dex files even if frameworks/base exists.

Bug: 133343287
Test: mainline modules build
Change-Id: I0647451420fd09bb680808b35e1ad3b8f514ba46
Merged-In: I0647451420fd09bb680808b35e1ad3b8f514ba46
(cherry picked from commit 9c74a1ee)