build: do not export compat functions from lib

build: do not export compat functions from lib

Commits 9db214527213 ("lib/gen-version-script.h: add getline and
getdelim to notmuch.sym if needed") and 3242e29e57ac ("build: add
canonicalize_file_name to symbols exported from libnotmuch.so")
started exporting compat functions from libnotmuch so that the cli
could use them. But we shouldn't export such functions from the
library. They are not part of our ABI. Instead, the cli should include
its own copies of the compat functions.