Try removing building C API specs in CRuby makefiles entirely

* Since it does not work when using some configure options such as:
  .../configure --with-ext=-test-/cxxanyargs,+ --enable-shared
  as the CI does.
* It also duplicates the logic of spec/ruby/optional/capi/spec_helper.rb incorrectly.
  ruby/spec maintainers have no experience and no interest in dealing with these complicated CRuby build system issues.
  We asked help on the CRuby Slack and nobody helped so far.

win32/Makefile.sub

@@ -1468,38 +1468,6 @@ loadpath: verconf.h
 	sed -e '1,/^const char ruby_initial_load_paths/d;/;/,$$d' \
 	    -e '/^^ /!d;s/ *"\\\\0"$$//;s/" *"//g'
 
-RUBYSPEC_CAPIEXT_SRCDIR = $(srcdir)/$(RUBYSPEC_CAPIEXT)
-RUBYSPEC_CAPIEXT_DEPS = $(RUBYSPEC_CAPIEXT_SRCDIR)/rubyspec.h $(RUBY_H_INCLUDES) $(LIBRUBY)
-RUBYSPEC_CAPIEXT_EXTS =
-
-!if [echo>rubyspec-capiext.mk RUBYSPEC_CAPIEXT_EXTS = \]
-!else if [for %I in ($(RUBYSPEC_CAPIEXT_SRCDIR)\*_spec.c) do \
-	@echo. $$(RUBYSPEC_CAPIEXT)/%~nI.so \>>rubyspec-capiext.mk]
-!else if [echo. $$(empty)>>rubyspec-capiext.mk]
-!else
-! include rubyspec-capiext.mk
-! if [del rubyspec-capiext.mk > nul]
-! endif
-!endif
-
-$(RUBYSPEC_CAPIEXT_EXTS): $(RUBYSPEC_CAPIEXT_DEPS)
-rubyspec-capiext: $(RUBYSPEC_CAPIEXT_EXTS)
-	@ $(NULLCMD)
-
-{$(RUBYSPEC_CAPIEXT_SRCDIR)}.c{$(RUBYSPEC_CAPIEXT)}.so:
-	$(ECHO) building $(@F)
-	$(Q)$(MAKEDIRS) $(@D)
-	$(Q)(echo EXPORTS&&echo Init_$(*F))> $*.def
-	$(Q)$(LDSHARED) -Fe$(@) -Fo$(*).obj $(INCFLAGS) $(CFLAGS) $(CPPFLAGS) $< $(LIBRUBYARG) -link $(DLDFLAGS) $(XLDFLAGS) $(LIBS) $(LOCAL_LIBS) -implib:$*.lib -pdb:$*.pdb -def:$*.def
-!if defined(LDSHARED_0)
-	$(Q)$(LDSHARED_0)
-	$(Q)$(LDSHARED_1)
-	$(Q)$(LDSHARED_2)
-!endif
-	$(Q)$(RM) $*.def $*.exp $*.lib $*.obj $*.pdb
-
-exts: rubyspec-capiext
-
 yesterday:
 	for /f "usebackq" %H in \
 	    (`$(GIT) -C $(srcdir) log -1 "--before=00:00+0900" "--format=%H"`) do \