tests: delete libhostname.so and chkhostname

Before this patch, `libhostname.so` and `chkhostname` were a test
facility for overriding `gethostname()` in non-debug builds on
Linux and other Unix platforms supporting `LD_PRELOAD`.

`gethostname()` has a single use with SMTP.

The alternative way to override `gethostname()` is building in debug
mode, which allows to do this via the `CURL_GETHOSTNAME` env, on all
platforms.

Drop the `LD_PRELOAD` solution in favour of the above.

Also:
- delete inactive NTLM code with a `gethostname()` call made from it.
- streamline NTLM code by dropping a `printf()` and a macro.
- tests: stop setting `CURL_GETHOSTNAME` where unnecessary.

Closes #14695

tests/libtest/Makefile.inc

@@ -38,7 +38,7 @@ TIMEDIFF = ../../lib/timediff.c ../../lib/timediff.h
 SUPPORTFILES = $(TIMEDIFF) first.c test.h
 
 # These are all libcurl test programs
-noinst_PROGRAMS = chkhostname libauthretry libntlmconnect libprereq      \
+noinst_PROGRAMS = libauthretry libntlmconnect libprereq                  \
  lib500 lib501 lib502 lib503 lib504 lib505 lib506 lib507 lib508 lib509   \
  lib510 lib511 lib512 lib513 lib514 lib515 lib516 lib517 lib518 lib519   \
  lib520 lib521 lib523 lib524 lib525 lib526 lib527 lib529 lib530 lib532   \
@@ -80,10 +80,6 @@ noinst_PROGRAMS = chkhostname libauthretry libntlmconnect libprereq      \
  lib3010 lib3025 lib3026 lib3027 \
  lib3100 lib3101 lib3102 lib3103
 
-chkhostname_SOURCES = chkhostname.c ../../lib/curl_gethostname.c
-chkhostname_LDADD = @CURL_NETWORK_LIBS@
-chkhostname_DEPENDENCIES =
-
 libntlmconnect_SOURCES = libntlmconnect.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
 libntlmconnect_LDADD = $(TESTUTIL_LIBS)