fixup: Remove useless line in test and rename test file itself

Author: mylai-mtk

clang/test/Preprocessor/riscv-cf-protection.c renamed to clang/test/Preprocessor/riscv-cf-protection-branch.c

@@ -146,5 +146,3 @@
 // NO-MACRO-NOT: __riscv_landing_pad
 // NO-MACRO-NOT: __riscv_landing_pad_unlabeled
 // NO-MACRO-NOT: __riscv_landing_pad_func_sig
-
-int main() { return 0; }