Stop looking for buck2 in the top-level ExecuTorch build (#13393)

We should no longer require buck for the main build. (Note that
scripts/build_apple_frameworks.sh still requires it for a custom script,
and the following PR will attempt to clean up mentions of BUCK2 from
scripts.)

Author: swolchok

CMakeLists.txt

@@ -79,11 +79,6 @@ if(NOT PYTHON_EXECUTABLE)
 endif()
 announce_configured_options(PYTHON_EXECUTABLE)
 
-if(NOT BUCK2)
-  resolve_buck2()
-endif()
-announce_configured_options(BUCK2)
-
 announce_configured_options(CMAKE_CXX_COMPILER_ID)
 announce_configured_options(CMAKE_TOOLCHAIN_FILE)
 announce_configured_options(BUILD_TESTING)

tools/cmake/Utils.cmake

@@ -119,74 +119,6 @@ function(extract_sources sources_file)
   endif()
 endfunction()
 
-# Sets the value of the BUCK2 variable by searching for a buck2 binary with the
-# correct version.
-#
-# The resolve_buck.py script uses the following logic to find buck2: 1) If BUCK2
-# argument is set explicitly, use it. Warn if the version is incorrect. 2) Look
-# for a binary named buck2 on the system path. Take it if it is the correct
-# version. 3) Check for a previously downloaded buck2 binary (from step 4). 4)
-# Download and cache correct version of buck2.
-function(resolve_buck2)
-  if(EXECUTORCH_ROOT)
-    set(executorch_root ${EXECUTORCH_ROOT})
-  else()
-    set(executorch_root ${CMAKE_CURRENT_SOURCE_DIR})
-  endif()
-
-  set(resolve_buck2_command
-      ${PYTHON_EXECUTABLE} ${executorch_root}/tools/cmake/resolve_buck.py
-      --cache_dir=${executorch_root}/buck2-bin
-  )
-
-  if(NOT ${BUCK2} STREQUAL "")
-    list(APPEND resolve_buck2_command --buck2=${BUCK2})
-  endif()
-
-  execute_process(
-    COMMAND ${resolve_buck2_command}
-    OUTPUT_VARIABLE resolve_buck2_output
-    ERROR_VARIABLE resolve_buck2_error
-    RESULT_VARIABLE resolve_buck2_exit_code
-    WORKING_DIRECTORY ${executorch_root}
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-  )
-
-  # $BUCK2 is a copy of the var from the parent scope. This block will set
-  # $buck2 to the value we want to return.
-  if(resolve_buck2_exit_code EQUAL 0)
-    set(buck2 ${resolve_buck2_output})
-    message(STATUS "Resolved buck2 as ${resolve_buck2_output}.")
-  elseif(resolve_buck2_exit_code EQUAL 2)
-    # Wrong buck version used. Stop here to ensure that the user sees the error.
-    message(FATAL_ERROR "Failed to resolve buck2.\n${resolve_buck2_error}")
-  else()
-    # Unexpected failure of the script. Warn.
-    message(WARNING "Failed to resolve buck2.")
-    message(WARNING "${resolve_buck2_error}")
-
-    if("${BUCK2}" STREQUAL "")
-      set(buck2 "buck2")
-    endif()
-  endif()
-
-  # Update the var in the parent scope. Note that this does not modify our local
-  # $BUCK2 value.
-  set(BUCK2
-      "${buck2}"
-      PARENT_SCOPE
-  )
-
-  # The buck2 daemon can get stuck. Killing it can help.
-  message(STATUS "Killing buck2 daemon")
-  execute_process(
-    # Note that we need to use the local buck2 variable. BUCK2 is only set in
-    # the parent scope, and can still be empty in this scope.
-    COMMAND "${buck2} killall"
-    WORKING_DIRECTORY ${executorch_root} COMMAND_ECHO STDOUT
-  )
-endfunction()
-
 # Sets the value of the PYTHON_EXECUTABLE variable to 'python' if in an active
 # (non-base) conda environment, and 'python3' otherwise. This maintains
 # backwards compatibility for non-conda users and avoids conda users needing to