tests/server: drop memdebug option

I added it just in case when removing enabled-by-default memdebug
from test servers. Apparently it broke after recent changes. It's
probably not a widely used feature and does not seem to be worth fixing.
It creates odd dependencies as the error message indicates:

```
[28/54] Building C object tests/server/CMakeFiles/servers.dir/__/__/lib/memdebug.c.obj
FAILED: tests/server/CMakeFiles/servers.dir/__/__/lib/memdebug.c.obj
[...]
lib/memdebug.c: In function 'curl_dbg_log':
lib/memdebug.c:465:12: error: implicit declaration of function 'mvsnprintf'; did you mean 'vsnprintf'? [-Wimplicit-function-declaration]
  465 |   nchars = mvsnprintf(buf, sizeof(buf), format, ap);
      |            ^~~~~~~~~~
      |            vsnprintf
lib/memdebug.c:465:12: warning: nested extern declaration of 'mvsnprintf' [-Wnested-externs]
```

This patch is dropping these build options:
- cmake: `ENABLE_SERVER_DEBUG`
- autotools: `--enable-server-debug` / `--disable-server-debug`

Follow-up to a16485a42e #16705

Closes #17629

tests/server/CMakeLists.txt

@@ -22,15 +22,10 @@
 #
 ###########################################################################
 
-# Get BUNDLE, BUNDLE_SRC, FIRSTFILES, UTILS, MEMDEBUG, CURLX_SRCS, TESTFILES variables
+# Get BUNDLE, BUNDLE_SRC, FIRSTFILES, UTILS, CURLX_SRCS, TESTFILES variables
 curl_transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 
-set(_sources_extra "")
-if(ENABLE_SERVER_DEBUG AND ENABLE_CURLDEBUG)
-  list(APPEND _sources_extra ${MEMDEBUG})
-endif()
-
 add_custom_command(
   OUTPUT "${BUNDLE_SRC}"
   COMMAND ${PERL_EXECUTABLE} "${PROJECT_SOURCE_DIR}/scripts/mk-unity.pl"
@@ -51,9 +46,6 @@ target_include_directories(servers PRIVATE
   "${PROJECT_SOURCE_DIR}/tests/server"  # for "first.h"
 )
 target_link_libraries(servers ${CURL_LIBS})
-if(ENABLE_SERVER_DEBUG)
-  set_property(TARGET servers APPEND PROPERTY COMPILE_DEFINITIONS "${CURL_DEBUG_MACROS}")
-endif()
 set_property(TARGET servers APPEND PROPERTY COMPILE_DEFINITIONS "WITHOUT_LIBCURL" "CURL_NO_OLDIES")
 # Test servers simply are standalone programs that do not use libcurl
 # library.  For convenience and to ease portability of these servers,

tests/server/Makefile.am

@@ -40,7 +40,7 @@ AM_CPPFLAGS = -I$(top_srcdir)/include        \
               -I$(top_srcdir)/src            \
               -I$(top_srcdir)/tests/server
 
-# Get BUNDLE, BUNDLE_SRC, FIRSTFILES, UTILS, MEMDEBUG, CURLX_SRCS, TESTFILES variables
+# Get BUNDLE, BUNDLE_SRC, FIRSTFILES, UTILS, CURLX_SRCS, TESTFILES variables
 include Makefile.inc
 
 EXTRA_DIST = CMakeLists.txt .checksrc $(FIRSTFILES) $(UTILS) $(TESTFILES)
@@ -53,14 +53,6 @@ LIBS = $(BLANK_AT_MAKETIME)
 if DOING_NATIVE_WINDOWS
 AM_CPPFLAGS += -DCURL_STATICLIB
 endif
-if ENABLE_SERVER_DEBUG
-if DEBUGBUILD
-AM_CPPFLAGS += -DDEBUGBUILD
-endif
-if CURLDEBUG
-AM_CPPFLAGS += -DCURLDEBUG
-endif
-endif
 
 AM_CPPFLAGS += -DWITHOUT_LIBCURL -DCURL_NO_OLDIES
 
@@ -69,12 +61,6 @@ $(BUNDLE_SRC): $(top_srcdir)/scripts/mk-unity.pl Makefile.inc $(FIRSTFILES) $(UT
 
 noinst_PROGRAMS = $(BUNDLE)
 nodist_servers_SOURCES = $(BUNDLE_SRC)
-servers_SOURCES =
-if ENABLE_SERVER_DEBUG
-if CURLDEBUG
-servers_SOURCES += $(MEMDEBUG)
-endif
-endif
 servers_LDADD = @CURL_NETWORK_AND_TIME_LIBS@
 servers_CFLAGS = $(AM_CFLAGS)
 CLEANFILES = $(BUNDLE_SRC)

tests/server/Makefile.inc

@@ -32,10 +32,6 @@ FIRSTFILES = first.c first.h
 # Common files used by test programs
 UTILS = getpart.c getpart.h util.c util.h
 
-MEMDEBUG = \
-  ../../lib/memdebug.c \
-  ../../lib/memdebug.h
-
 CURLX_SRCS = \
   ../../lib/curlx/base64.c \
   ../../lib/curlx/inet_pton.c \