SDL copies MOBILE_API.xml from 'rpc_spec' submodule during build process

[dboltovskyi]

Bug Report

According to #3270 Core build process performs redundant copy operation of MOBILE_API.xml file from submodule rpc_spec to sdl_core sources (/tools/rpc_spec -> src/components/interfaces)

Reproduction Steps

1. Try to build SDL Core
2. Check content of src/components/interfaces folder

Expected Behavior

There is no MOBILE_API.xml file

Observed Behavior

There is redundant MOBILE_API.xml file

OS & Version Information

• OS/Version: Ubuntu 18.04/20.04
• SDL Core Version: https://github.com/smartdevicelink/sdl_core/tree/release/8.0.0 (de58a41)

[iCollin]

Closed via #3778