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/data/test1310

@@ -65,10 +65,6 @@ http
 HTTP with NTLM delegation to winbind helper
 </name>
  <setenv>
-# we force our own host name, in order to make the test machine independent
-CURL_GETHOSTNAME=curlhost
-# we try to use the LD_PRELOAD hack, if not a debug build
-LD_PRELOAD=%PWD/libtest/.libs/libhostname.so
 # set path to fake_auth instead of real ntlm_auth to generate NTLM type1 and type 3 messages
 CURL_NTLM_WB_FILE=%PWD/server/fake_ntlm
 # set source directory so fake_ntlm can find the test files
@@ -81,9 +77,6 @@ CURL_NTLM_AUTH_TESTNUM=%TESTNUMBER
 <command>
 http://%HOSTIP:%HTTPPORT/%TESTNUMBER -u testuser:anypasswd --ntlm-wb
 </command>
-<precheck>
-chkhostname curlhost
-</precheck>
 </client>
 
 # Verify data after the test has been "shot"