bp2build: Remove duplicate system shared libs

If a system shared lib is specified in shared_libs, this results in
duplicate values appearing, causing a failure in Bazel. This change
removes any system shared libraries that appear in shared libraries from
bionic OS axes where system_shared_libraries takes the default value.

Test: go soong tests
Test: temporarily allowlist directory with this issue, no longer hits
      duplicate library failure.
Change-Id: I9dce570b73c24973f695b815bce8d50f7259798d