Remove duplicated sources that go into hiddenapi-mappins

framework-srcs are already coming from metalava-api-stubs-default (via
framework-minus-apex). We don't need to give framework-srcs again.

Test: choosecombo into sdk_phone_arm7
Test: m
out/soong/.intermediates/frameworks/base/hiddenapi-mappings/android_common/api-versions.xml
out/soong/.intermediates/frameworks/base/hiddenapi-mappings/android_common/dex-mapping.txt
out/soong/.intermediates/frameworks/base/hiddenapi-mappings/android_common/hiddenapi-mappings-stubs.srcjar
out/soong/.intermediates/frameworks/base/hiddenapi-mappings/android_common/hiddenapi-mappings_annotations.zip
is successful

Change-Id: I9ea6e06e8bd388f3a495acb6ff5555c0ce2f75b2