[rust] [coverage] Don't pass -C link-dead-code

Bug: http://b/186873963

Per jgalenson@, this was added for GCOV and is not needed for clang
coverage.

Test: http://go/abtd/run/L71000000950546158
Change-Id: I352669687cbe764d938acb94d9d4fe0c24a31a56