Remove iwyu from Travis CI files

Change-Id: I02fe6a8a44dfcbb829ac16e61164b3d5d7ad436b

ci/travis_script_cpp.sh

@@ -29,8 +29,6 @@ pushd $CPP_BUILD_DIR
 
 $TRAVIS_MAKE lint
 
-$TRAVIS_MAKE iwyu
-
 # ARROW-209: checks depending on the LLVM toolchain are disabled temporarily
 # until we are able to install the full LLVM toolchain in Travis CI again
 

ci/travis_script_python.sh

@@ -75,8 +75,6 @@ function rebuild_arrow_libraries() {
   ninja
   ninja install
 
-  ninja iwyu
-
   popd
 }
 

cpp/CMakeLists.txt

@@ -583,9 +583,9 @@ endif()
 ############################################################
 # "make iwyu" target
 ############################################################
-if (UNIX)
-add_custom_target(iwyu ${BUILD_SUPPORT_DIR}/iwyu/iwyu.sh)
-endif (UNIX)
+if(UNIX)
+  add_custom_target(iwyu ${BUILD_SUPPORT_DIR}/iwyu/iwyu.sh)
+endif(UNIX)
 
 ############################################################
 # Linker and Dependencies