Remove api_dir property

The api_dir property is removed, and the api dir path for aidl_interface
is fixed to aidl_api/{module_name}. According to this rule, all api dirs
are moved to aidl_api/{module_name}.

Bug: 113134692
Test: m -j
Change-Id: I0feb7b6c6b2ee8620e0e1b7c07c409a294e3a9d2
Merged-In: I0feb7b6c6b2ee8620e0e1b7c07c409a294e3a9d2
(cherry picked from commit d1dcab92)