cmake: remove redundant default optimization level

- user can prepend compiler options with CFLAGS="-g -O2" cmake ...

cmake/compiler-specific.cmake

@@ -13,11 +13,6 @@ if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
   if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
     target_compile_definitions(common INTERFACE CC_GCC_LIKE_ASM)
 
-    target_compile_options(
-      common INTERFACE -O0
-                       # <$<$<BOOL:${PROFILE}>:-pg>
-    )
-
     target_compile_options(
       common
       INTERFACE -Wall -funroll-loops -Wcast-align