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

lib/curl_gethostname.c

@@ -39,15 +39,6 @@
  *
  * Note: The function always returns the un-qualified hostname rather
  * than being provider dependent.
- *
- * For libcurl shared library release builds the test suite preloads
- * another shared library named libhostname using the LD_PRELOAD
- * mechanism which intercepts, and might override, the gethostname()
- * function call. In this case a given platform must support the
- * LD_PRELOAD mechanism and additionally have environment variable
- * CURL_GETHOSTNAME set in order to override the returned hostname.
- *
- * For libcurl static library release builds no overriding takes place.
  */
 
 int Curl_gethostname(char * const name, GETHOSTNAME_TYPE_ARG2 namelen)
@@ -78,9 +69,6 @@ int Curl_gethostname(char * const name, GETHOSTNAME_TYPE_ARG2 namelen)
 
 #else /* DEBUGBUILD */
 
-  /* The call to system's gethostname() might get intercepted by the
-     libhostname library when libcurl is built as a non-debug shared
-     library when running the test suite. */
   name[0] = '\0';
   err = gethostname(name, namelen);