Normalize target path for license dependencies.

If not normalized the same as declare-license-metadata, two rules get
generated instead of one rule with both license text and deps.

Test: m droid dist

Test: build/soong/soong_ui.bash --make-mode TARGET_PRODUCT=sdk TARGET_BUILD_VARIANT=userdebug sdk dist sdk_repo

Change-Id: I3a8f2d3825c8c0183049fa12b14ace9b54066a01
Merged-in: I3a8f2d3825c8c0183049fa12b14ace9b54066a01