Always default to 1.9 for host java modules in Android.mk files

Host modules shouldn't use the logic for device modules to determine
the java language version to use, always default to 1.9.

Cherry-pick from https://r.android.com/1892956 - this may be necessary
in sc-mainline-prod when it switches to prebuilt SDKs (b/204189791).

Bug: 202761304
Test: presubmits
Change-Id: I268dd34d887db4646e188858c7f2aedc30966856
Merged-In: I268dd34d887db4646e188858c7f2aedc30966856