Signature rework (#2033)

* init

* incremental

* cleanup

Author: chenmoneygithub

dspy/signatures/__init__.py

@@ -2,7 +2,6 @@
 from dspy.signatures.signature import (
     SignatureMeta,
     Signature,
-    update_signatures,
     ensure_signature,
     make_signature,
     infer_prefix,
@@ -18,7 +17,6 @@
     "SignatureMeta",
     "Signature",
     "infer_prefix",
-    "update_signatures",
     "ensure_signature",
     "make_signature",
 ]