Cleanup CRefine Wellformed_C

[Xaphiosis]

During work on AArch64 CRefine, we identified the following aspects of cleanup in Wellformed_C.thy which should be applied across all platforms once AARCH64 CRefine theories make their way into master:

• old-style definitions/abbreviations/etc; re-styling will also shorten the file (less wasted vertical space)
• remove unused is<cap-type>Cap_C lemmas, e.g. isNotificationCap_C
• remove unused <ko type>_at_C' definitions, e.g. ep_at_C'
• remove unused capUntypedPtr_C definition