Move apicheck.mk off SRC_API_DIR.

This directory is getting deleted.

Also remove the variable, the other uses are being removed in this cl:
I1d4e87e7840e979b83779a2aefe176e7c1ed1527

Bug: 77525052
Test: Verified value of last_released_sdk_version variable.
Change-Id: I69b10ad83a8c06d337606df91e8d3b604adfef70