fix: remove hardcoded AVM_TRANSPILER_LIB from debug CMake preset (#21884)

## Summary

Fixes the nightly barretenberg debug build that has been failing since
2026-03-20.

The `debug` CMake preset hardcoded `AVM_TRANSPILER_LIB` pointing to
`libavm_transpiler.a`, but the nightly debug CI job sets
`AVM_TRANSPILER=0` which skips building that library. When the build
cache expired (due to code changes in PR #21835), the fresh build failed
at link time because the `.a` file doesn't exist.

Removing `AVM_TRANSPILER_LIB` from the debug preset lets it inherit from
`default` (which doesn't set it), matching the CI's `AVM_TRANSPILER=0`
intent.

Full analysis:
https://gist.github.com/AztecBot/c76c930ef9446eda7a20616035b6e60a

## Test plan
- [x] Debug build compiles (1108 targets)
- [x] commitment_schemes_tests pass (88/88)
- [x] ultra_honk_tests, sumcheck_tests, honk_tests, hypernova_tests,
goblin_tests, flavor_tests all pass

ClaudeBox log: https://claudebox.work/s/5fc7d037bce53386?run=1

Author: ludamad

barretenberg/cpp/CMakePresets.json

@@ -94,7 +94,6 @@
         "LDFLAGS": "-gdwarf-4"
       },
       "cacheVariables": {
-        "AVM_TRANSPILER_LIB": "${sourceDir}/../../avm-transpiler/target/release/libavm_transpiler.a",
         "CMAKE_BUILD_TYPE": "Debug",
         "ENABLE_ASAN": "OFF",
         "DISABLE_ASM": "OFF",