memory: stop overriding unused wcsdup()/_wcsdup() system functions

[vszakats]

Also ban them via checksrc.

The code continues to use _tcsdup().

Assisted-by: Daniel Stenberg

Closes #17840

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• part of this PR moved to windows: drop redundant curl_wcsdup_callback callback #17843

[vszakats]

Into the rabbit hole:
76e047f #7540
changed the initial value of Curl_cwcsdup from _wcsdup to Curl_wcsdup.
It did not apply the same change to global_init() a few lines below.
libtests also remains using _wcsdup.

Is this correct? Aren't all these supposed to be in sync?

[vszakats]

Same has been reported last year under the original PR:
#7540 (comment)

[bagder]

It looks like _tcsdup() is the only call left used in libcurl code, in four different places.

[vszakats]

Indeed!

Except when assigning the function to Curl_cwcsdup. Which still uses _wcsdup:

curl/tests/libtest/memptr.c

Lines 43 to 45 in f048546

	#if defined(_WIN32) && defined(UNICODE)
	curl_wcsdup_callback Curl_cwcsdup = wcsdup;
	#endif

curl/lib/easy.c

Lines 160 to 162 in f048546

	#if defined(_WIN32) && defined(UNICODE)
	Curl_cwcsdup = (curl_wcsdup_callback)_wcsdup;
	#endif

As opposed to this fixed instance:

curl/lib/easy.c

Lines 132 to 134 in f048546

	#if defined(_WIN32) && defined(UNICODE)
	curl_wcsdup_callback Curl_cwcsdup = Curl_wcsdup;
	#endif

[bagder]

Except when assigning the function to Curl_cwcsdup.

I was only referring to callers, users of this functionality.

[vszakats]

Got it now!

So, deleted both macro redefs, since those are necessary for actual calls,
which do not exist.

Then fixed to use Curl_wcsdup() in global_init() (will move this to
separate PR), and changed the same in libtests to map to _wcsdup
instead of wcsdup.