simplifying lint headers script (#4802)

ci/lintHeaders.sh

@@ -4,26 +4,19 @@
 # an MPL license header.
 # $ lintHeaders ./src *.rs
 
-license1="/* This Source Code Form is subject to the terms of the Mozilla Public"
-license2=" * License, v. 2.0. If a copy of the MPL was not distributed with this"
-license3=" * file, You can obtain one at https://mozilla.org/MPL/2.0/. */"
+license="/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */"
 
-files=$(find $1 -type f -name '*.rs')
-result=0
-
-headerLineNumbers() {
-   grep -Fn -e "$license1" -e "$license2" -e "$license3" "$1" | cut -f1 -d:
-}
+files=$(find $1 -type f -name $2)
 
-expectedHeaderLineNumbers='1
-2
-3'
+result=0
 
-for file in $files; do
-  if ! [ "$(headerLineNumbers $file)" = "$expectedHeaderLineNumbers" ]; then
-    echo "$file"
+for file in ${files[@]}; do
+  if ! [ "$(head $file -n3)" = "$license" ]; then
+    echo "Incorrect header in $file"
     result=1
   fi
 done
 
-exit $result
+exit $result