Fix REF1 to behave analogous to the other REF macros

REF1 is currently only used once in entire DRuntime and Phobos, so maybe
a special OBJECTREF macro would have been better?
Anyhow, have a look at the only use of `REF1` to understand the
motivation for this PR:

https://dlang.org/phobos/std_file.html#.thisExePath

Also there are three other PRs being blocked on this:

- dlang/dmd#7342
- dlang/druntime#2082
- dlang/phobos#6140

dlang.org.ddoc

@@ -365,7 +365,7 @@ $(COMMENT
     (the phobos path can be different, of course).
 )
 REF=<a href="$(PHOBOS_PATH)$2$(UNDERSCORE_PREFIXED_SKIP $+).html#.$1">$(D $2$(DOT_PREFIXED_SKIP $+, $1))</a>
-REF1=<a href="$(PHOBOS_PATH)$2.html#.$1">$(D $2)</a>
+REF1=<a href="$(PHOBOS_PATH)$2.html#.$1">$(D $1)</a>
 _=
 
 $(COMMENT