libstdc++-trusty: Update license file name

The NOTICE symlink in libcxx was removed.
Replace it with its target LICENSE.TXT in
the libstdc++-trusty build.

Bug: 304585390
Test: build.py generic-x86_64-test
Change-Id: I898dddfb2a22f7a3aa8a6dd5baeb1d7dca8acd8d
1 file changed