fix: Remove dead and broken basedir() from _helpers.bash

basedir() had a broken escape ($(dirname \"$-2\") makes no sense) and
was never called anywhere in the repo — it's a leftover copy of the
already-deprecated libs.deprecated/basedir.bash. bashrc already has
its own get_script_dir() for the same need, with proper symlink
resolution.

_helpers.bash

@@ -1,7 +1,3 @@
-function basedir() {
-	(cd "$(dirname \"$-2\")" && pwd)
-}
-
 function _source_file_if_exists() {
 	if [ -r "$1" ]; then
 		test -n "${DEBUG_BASHRC}" && echo "-- Sourcing file $1"