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: I87ff4b5840e6bacacd76ead90290df2f15b205d5