EXSLT function str:replace() is broken as-is

the str:replace() function is no longer usable without a transform
context. I take it from the bug report that it is not supposed to be used
from plain XPath but only from XSLT according to the EXSLT specification.

However, the previous implementation used to work in XPath and is still
registered on an xmlXPathContext by the exsltStrXpathCtxtRegister()
function. When called from plain XPath, it results in a memory error in
line 526 (exsltStrReturnString()) of strings.c because xsltCreateRVT()
returns NULL as an error indicator due to a NULL transform context being
passed in, which was the return value from xsltXPathGetTransformContext() a
bit further up (and the code doesn't validate that).

Since fixing the function looks impossible, best is to remove it.
Fix quoting of xlocale test program in configure.in

Double square brackets aren't needed anymore, probably due to the
changes in commit a2cd8a03.