Remove dylibs prop from rust module types

For device build, rust defaults to dylib linkage for rustlibs deps. `dylibs` prop was provided for flexibility.

By removing it, we're enforcing users to either use the default linkage (dylibs for device and rlibs for host) or rlibs prop explicitly. This means no dylibs for host modules. This makes sense because host modules always uses rlib linkage against libstd. The flexibility with dylibs prop opened room for linkage collisions because the dependencies don't link against libstd the same way.

Test: go test
Change-Id: I2fc221daa8a9bb42bdcf6d9823c723a4ddabe7b5