MINOR: Don't uninstall Flatbuffers in CI (#711)

## What's Changed

There is no more need after
apache/arrow@32641ec

Also, disable building tests to avoid issues with Boost/Homebrew. They aren't executed anyways.

Author: lidavidm

.github/workflows/rc.yml

@@ -261,11 +261,6 @@ jobs:
           # bundled Protobuf.
           brew uninstall protobuf
 
-          # We need Flatbuffers 24, not the latest version
-          # Homebrew does not offer older versions, so remove the Homebrew
-          # package and rely on Arrow using a bundled version instead
-          brew uninstall flatbuffers
-
           brew bundle --file=Brewfile
       - name: Prepare ccache
         run: |

ci/scripts/jni_macos_build.sh

@@ -61,7 +61,7 @@ github_actions_group_begin "Building Arrow C++ libraries"
 install_dir="${build_dir}/cpp-install"
 : "${ARROW_ACERO:=ON}"
 export ARROW_ACERO
-: "${ARROW_BUILD_TESTS:=ON}"
+: "${ARROW_BUILD_TESTS:=OFF}"
 export ARROW_BUILD_TESTS
 : "${ARROW_DATASET:=ON}"
 export ARROW_DATASET

ci/scripts/jni_manylinux_build.sh

@@ -57,7 +57,7 @@ devtoolset_version="$(rpm -qa "devtoolset-*-gcc" --queryformat '%{VERSION}' | gr
 devtoolset_include_cpp="/opt/rh/devtoolset-${devtoolset_version}/root/usr/include/c++/${devtoolset_version}"
 : "${ARROW_ACERO:=ON}"
 export ARROW_ACERO
-: "${ARROW_BUILD_TESTS:=ON}"
+: "${ARROW_BUILD_TESTS:=OFF}"
 export ARROW_BUILD_TESTS
 : "${ARROW_DATASET:=ON}"
 export ARROW_DATASET