test: remove unused filter functions

They've been unused since their introduction in commit 0083854b12
("Copy test framework from Git").

test/test-lib.sh

@@ -267,33 +267,6 @@ export GNUPGHOME="${TEST_TMPDIR}/gnupg"
 trap 'trap_exit' EXIT
 trap 'trap_signal' HUP INT TERM
 
-test_decode_color () {
-	sed	-e 's/.\[1m/<WHITE>/g' \
-		-e 's/.\[31m/<RED>/g' \
-		-e 's/.\[32m/<GREEN>/g' \
-		-e 's/.\[33m/<YELLOW>/g' \
-		-e 's/.\[34m/<BLUE>/g' \
-		-e 's/.\[35m/<MAGENTA>/g' \
-		-e 's/.\[36m/<CYAN>/g' \
-		-e 's/.\[m/<RESET>/g'
-}
-
-q_to_nul () {
-	perl -pe 'y/Q/\000/'
-}
-
-q_to_cr () {
-	tr Q '\015'
-}
-
-append_cr () {
-	sed -e 's/$/Q/' | tr Q '\015'
-}
-
-remove_cr () {
-	tr '\015' Q | sed -e 's/Q$//'
-}
-
 # Generate a new message in the mail directory, with a unique message
 # ID and subject. The message is not added to the index.
 #