system/rust/gatt: Switch to the default PDL rust generator

The generator rust_no_alloc is no longer maintained and the
default rust generator is now the preferred rust generator.

Bug: 331817295
Test: m com.android.btservices
Test: atest --host libbluetooth_core_rs_test
Flag: EXEMPT, mechanical refactor
Change-Id: I18da339ffb2537229fb870594edd344b6a924241