test: consolidate definition of $LF

As we seem to need this variable that holds a single LF character
in many places, define it in test-lib.sh and let the test scripts
use it.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t1013-loose-object-format.sh

@@ -26,8 +26,6 @@ standard format, deflated with 4KB window size: Agit/JGit on Android
 '
 
 . ./test-lib.sh
-LF='
-'
 
 assert_blob_equals() {
 	printf "%s" "$2" >expected &&

t/t1020-subdirectory.sh

@@ -17,8 +17,6 @@ test_expect_success setup '
 	cp one original.one &&
 	cp dir/two original.two
 '
-LF='
-'
 
 test_expect_success 'update-index and ls-files' '
 	git update-index --add one &&

t/t3902-quoted.sh

@@ -10,8 +10,6 @@ test_description='quoted output'
 FN='濱野'
 GN='純'
 HT='	'
-LF='
-'
 DQ='"'
 
 echo foo 2>/dev/null > "Name and an${HT}HT"

t/t7800-difftool.sh

@@ -10,9 +10,6 @@ Testing basic diff tool invocation
 
 . ./test-lib.sh
 
-LF='
-'
-
 remove_config_vars()
 {
 	# Unset all config variables used by git-difftool

t/test-lib.sh

@@ -92,6 +92,10 @@ _x40="$_x05$_x05$_x05$_x05$_x05$_x05$_x05$_x05"
 # Zero SHA-1
 _z40=0000000000000000000000000000000000000000
 
+# Line feed
+LF='
+'
+
 # Each test should start with something like this, after copyright notices:
 #
 # test_description='Description of this test...