remove unnecessary ccgutils dependency

[zerbina]

Summary

Remove an obsolete usage of ccgIntroducedPtr from sem, breaking an
import dependency between sem and the code generator, and allowing for
ccgIntroducedPtr to move back to ccgtypes.

Details

It was originally possible for the arguments to a copy hook overlapping
in memory (a parameter aliasing violation), resulting in incorrect
behaviour when copying variant objects if they do.

ed12679 worked around this by checking
whether both parameters were (hidden) pointers to the same location,
skipping the copy if they are, with ccgIntroducedPtr used to check
whether the source parameter is passed as via a pointer indirection.

This is a layering violation, and also no longer necessary, since
injecthooks ensures that the immutable argument doesn't refer to the
same memory location as the mutable one -- the workaround in
liftdestructors can thus be removed.

[saem]

/merge

[github-actions]

Merge requested by: @saem

Contents after the first section break of the PR description has been removed and preserved below:

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Notes for Reviewers

• a preparation for the MIR type IR; ccgIntroducedPtr being in ccgutils limits its implementation