Remove unneeded #includes

HTMLparser.c

include/libxml/SAX.h

include/libxml/SAX2.h

include/libxml/parser.h

parser.c

parserInternals.c

testHTML.c

testOOM.c

testOOMlib.h

testReader.c

testSAX.c

testXPath.c

threads.c

xlink.c

xmlmemory.c

xmlregexp.c

xpath.c