Drop prefer: true from com.android.apex.cts.shim.v1_prebuilt
The value of `prefer` for `com.android.apex.cts.shim.v1_prebuilt` is a
no-op becauase we do not have a source apex named
`com.android.apex.cts.shim.v1_prebuilt`.
Test: No functional change in .ninja file before and after change, but
there are some metadata changes about file pos like such
```
< # Defined: system/apex/shim/Android.bp:90:1
> # Defined: system/apex/shim/Android.bp:89:1
```
Change-Id: Ib48b3a5880ed4d19dcc8ea54ba35a9a67ed54338
1 file changed
