Arm backend: Remove special host build of flatcc (#11278)

### Summary
This was a workaround as host version of flattcc was not generated from
the build as it should and you got the target version. Later when
flattcc was needed on the host it was the wrong version and you got an
error.
Now this has been solved in the project and flattcc is only build for
the host so there is no need to force a special build like this anymore.

### Test plan
Tested in local build and on GitHub

Signed-off-by: Zingo Andersen <[email protected]>

Author: zingo

backends/arm/scripts/build_executorch.sh

@@ -54,47 +54,9 @@ source ${setup_path_script}
 
 et_build_dir="${et_build_root}/cmake-out"
 
-# Used for flatcc host excutable if Devtools is used
-et_build_host_dir=${et_build_root}/cmake-out-host-tools
-
 set -x
 cd "${et_root_dir}"
 
-if [ "$build_with_etdump" = true ] ; then
-    ( set +x ;
-        echo "--------------------------------------------------------------------------------" ;
-        echo "Build ExecuTorch Libraries host flatcc bin ${build_type} into ${et_build_host_dir}/bin/flatcc" ;
-        echo "--------------------------------------------------------------------------------" )
-
-    # Build host flatcc bin
-    # This is a way to work around that the flatcc executable get build for target (e.g. Arm) later
-    # and get replaced. flatcc is a tool used on the host for etdump and BundleIO handling.
-    # The way to solve this is to generate it once for the host, then copy it to ${et_build_host_dir}/bin
-    # and later point that out with -DFLATCC_EXECUTABLE=${et_build_host_dir}/bin/flatcc later.
-
-    cmake                                                 \
-        -DCMAKE_INSTALL_PREFIX=${et_build_host_dir}       \
-        -DCMAKE_BUILD_TYPE=${build_type}                  \
-        -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=OFF            \
-        -DEXECUTORCH_ENABLE_LOGGING=ON                    \
-        -DEXECUTORCH_BUILD_ARM_BAREMETAL=ON               \
-        -DEXECUTORCH_BUILD_KERNELS_QUANTIZED=ON           \
-        -DEXECUTORCH_BUILD_EXTENSION_RUNNER_UTIL=ON       \
-        -DEXECUTORCH_BUILD_DEVTOOLS=ON                    \
-        -DEXECUTORCH_ENABLE_EVENT_TRACER=ON               \
-        -DFLATCC_ALLOW_WERROR=OFF                         \
-        -B"${et_build_host_dir}"                          \
-        "${et_root_dir}"
-
-    # third-party/flatcc/bin/flatcc gets build already in the in the cmake config step above
-    # so there is no cmake building step done
-
-    # Copy host flatcc excutable so it's saved when we build for target (Arm) later
-    et_build_host_dir=$(realpath ${et_build_host_dir})
-    mkdir -p ${et_build_host_dir}/bin
-    cp third-party/flatcc/bin/flatcc ${et_build_host_dir}/bin
-fi
-
 ( set +x ;
     echo "--------------------------------------------------------------------------------" ;
     echo "Build ExecuTorch target libs ${build_type} into '${et_build_dir}'" ;
@@ -111,8 +73,7 @@ if [ "$build_with_etdump" = true ] ; then
     build_with_etdump_flags="-DEXECUTORCH_BUILD_DEVTOOLS=ON                    \
                             -DEXECUTORCH_ENABLE_EVENT_TRACER=ON               \
                             -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=OFF      \
-                            -DFLATCC_ALLOW_WERROR=OFF                         \
-                            -DFLATCC_EXECUTABLE=${et_build_host_dir}/bin/flatcc "
+                            -DFLATCC_ALLOW_WERROR=OFF "
 fi
 
 echo "Building with Devtools: ${build_devtools_flags} ${build_with_etdump_flags}"