Fix redundant includes already in libexslt.h
Remove includes of "config.h", <libxslt/xsltconfig.h> and <libxml/xmlversion.h> in libexslt C sources since they are already included with "libexslt/libexslt.h".
Remove includes of "config.h", <libxslt/xsltconfig.h> and <libxml/xmlversion.h> in libexslt C sources since they are already included with "libexslt/libexslt.h".