[RNE Rewrite] fix(build): remove redundant flag to fix macro redefinition warning

[barhanc]

Description

Fixes a -Wmacro-redefined compiler warning emitted when building native C++ sources. Build configurations (podspec, CMakeLists.txt, and compile_flags.txt) were explicitly setting the compiler definition -DC10_USING_CUSTOM_GENERATED_MACROS=1. However, the vendored header Macros.h (third-party/include/torch/headeronly/macros/Macros.h) already defines #define C10_USING_CUSTOM_GENERATED_MACROS directly on line 1. Passing the preprocessor macro via compiler flags resulted in macro redefinition warning.

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

• Build example apps and verify that no macro redefinition warning is emitted.

Screenshots

Related issues

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes