check-copyright improvements (kokkos#6399)

* check-copyright now cleans up "header" and "header_diff" files

* These changes improve the performance of check-copyright by about 20%
(performance not rigorously tested).

scripts/docker/check_format_cpp.sh on an M2 Max Mac took about 34s
before these changes, and 28s afterwards.

* Shaved another 5s off the run time by piping directly into "diff"
instead of creating a temporary "header" file

* Update scripts/check-copyright

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

* Update scripts/check-copyright

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

* Update scripts/check-copyright

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

* Update scripts/check-copyright

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

* Update scripts/check-copyright

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

* Changed quoted variable names to have curly braces in them (for
consistent style)

---------

Co-authored-by: Cezary Skrzyński <czars1988@gmail.com>

scripts/check-copyright

@@ -1,16 +1,15 @@
-files=`git ls-files | grep -e '.*\.\(cc\|cpp\|hpp\)' | grep -v 'tpls/'`
+files=$(git ls-files | grep -e '.*\.\(cc\|cpp\|hpp\)' | grep -v 'tpls/')
 echo "" &> scripts/diff_files
-tmp=`cat LICENSE_FILE_HEADER | wc -l`
+tmp=$(wc -l < LICENSE_FILE_HEADER)
 NNEW=$(($tmp))
-for file in $files; do
-  head -n +$NNEW $file &> header
-  diff header LICENSE_FILE_HEADER &> header_diff
-  count=`cat header_diff | wc -l`
-  #echo $file " " COUNT " " $count >> diff_headers
-  if [ "$count" -ne "0" ]; then
-    echo $file >> scripts/diff_files
+for file in $files
+do
+  head -n +$NNEW "${file}" | diff -q - LICENSE_FILE_HEADER > /dev/null
+  if [[ "${?}" == 1 ]]
+  then
+    echo "${file}" >> scripts/diff_files
   fi
 done
 tmpfile=$(mktemp -t kokkos_diff_files.XXXX)
-cat scripts/diff_files | sort &> $tmpfile
-mv $tmpfile scripts/diff_files
+sort < scripts/diff_files &> "${tmpfile}"
+mv "${tmpfile}" scripts/diff_files