Fix AAPT path in dexpreopt.

Dexpreopt uses AAPT to parse `targetSdkVersion` from the manifest, so it
the generated dexpreopt.sh script that calls AAPT must depend on it,
otherwise AAPT might not be built by the time it is used. Tool
dependencies are handled via the global Soong config and the
DEXPREOPT_GEN_DEPS variable that Soong generates for Make. This config
always uses Soong tool paths, like out/soong/host/linux-x86/bin/aapt
rather than out/host/linux-x86/bin/aapt.

This CL fixes a mistake in dexpreopt rule that used context-dependent
AAPT path (so, when called from Make, the dependency was on Soong tool,
but a Make tool was actually used, so it failed sometimes).

Bug: 132357300
Test: lunch aosp_cf_x86_64_phone-userdebug && m
Change-Id: I1f0ab4afac98e6239f324e7f3571d670fd7a36cd