tidy-up: delete stray references from autotools, docs

- autotools: delete stray `VC14_LIB*` references.
- autotools: delete (now) empty `CLEANFILES`.
- autotools: delete no longer used lib/src .inc includes in root makefile.
- autotools: delete stray `cygwinbin` target.
- autotools: delete stray `pkgadd` target (Solaris).
- lib, src: delete stray files from `.gitignore`.
- INSTALL.md: delete reference to non-existing `src/config-win32.h`.
- lib/config-win32ce.h: whitespace.
- lib/config-win32ce.h: sync comments with `config-win32.h`.

Closes #15944

src/.gitignore

@@ -3,13 +3,8 @@
 # SPDX-License-Identifier: curl
 
 *.a
-*.nlm
 *.res
-config-win32.h
 curl
-curl_config.h
-curl_config.h.in
 stamp-h2
 tool_ca_embed.c
 tool_hugehelp.c
-tool_version.h.dist