Remove redundant renderscript_target_api computation

renderscript_target_api is set by java_renderscript.mk, it doesn't
need to be computed again in static_java_library.mk and
package_internal.mk.

Bug: 73885582
Test: no change to ninja file
Change-Id: Ib6e00be425c385f4911def19ed5042a740f2c79b