build: Remove tune-cpu for lts-cpu (#17912)

Author: ritchie46

.github/workflows/release-python.yml

@@ -141,7 +141,6 @@ jobs:
         # IMPORTANT: All features enabled here should also be included in py-polars/polars/_cpu_check.py
         run: |
           if [[ "$IS_LTS_CPU" = true ]]; then
-            TUNE_CPU=x86-64-v2
             FEATURES=+sse3,+ssse3,+sse4.1,+sse4.2,+popcnt,+cmpxchg16b
             CC_FEATURES="-msse3 -mssse3 -msse4.1 -msse4.2 -mpopcnt -mcx16"
           else
@@ -161,8 +160,13 @@ jobs:
           CC_FEATURES: ${{ steps.features.outputs.cc_features }}
           CFG: ${{ matrix.package == 'polars-lts-cpu' && '--cfg allocator="default"' || '' }}
         run: |
-          echo "RUSTFLAGS=-C target-feature=$FEATURES -Z tune-cpu=$TUNE_CPU $CFG" >> $GITHUB_ENV
-          echo "CFLAGS=$CC_FEATURES -mtune=$TUNE_CPU" >> $GITHUB_ENV
+          if [[ -z "$TUNE_CPU" ]]; then
+            echo "RUSTFLAGS=-C target-feature=$FEATURES $CFG" >> $GITHUB_ENV
+            echo "CFLAGS=$CC_FEATURES" >> $GITHUB_ENV
+          else
+            echo "RUSTFLAGS=-C target-feature=$FEATURES -Z tune-cpu=$TUNE_CPU $CFG" >> $GITHUB_ENV
+            echo "CFLAGS=$CC_FEATURES -mtune=$TUNE_CPU" >> $GITHUB_ENV
+          fi
 
       - name: Set variables in CPU check module
         run: |