Revert "Add function to catenate n copies of a string"

COMPHELPER_DLLPUBLIC of an inline function is wrong. Nevermind that I just
followed the example of the preceding functions.

And it is too bikeshedding-inducing anyway to use recursion.

This wasn't used anywahere yet anyway in committed code, just locally in a
tree of mine. Will add a local copy there.

This reverts commit ee0d7d4c.

include/comphelper/string.hxx

@@ -308,14 +308,6 @@ COMPHELPER_DLLPUBLIC inline OUStringBuffer& padToLength(
     return detail::padToLength(rBuffer, nLength, cFill);
 }
 
-COMPHELPER_DLLPUBLIC inline OUString duplicate(const OUString& rString, int nCopies)
-{
-    if (nCopies <= 0)
-        return OUString("");
-    else
-        return rString + duplicate(rString, nCopies-1);
-}
-
 /** Replace a token in a string
     @param rIn       OUString in which the token is to be replaced
     @param nToken    which nToken to replace