Updated pdf cache clear steps consistently with current pdfbox version

- Removed calls to no more existing clearResources functions (on PDFont
class and its children) since upgrade to pdfbox 2.n.n
- Removed hacky usage of protected internal ClassLoader function. This
removes the warnings displayed when running with JDK9 or JDK10 :

     [java] WARNING: Illegal reflective access by
net.yacy.document.parser.pdfParser$ResourceCleaner (file:<path>) to
method java.lang.ClassLoader.findLoadedClass(java.lang.String)
     [java] WARNING: Please consider reporting this to the maintainers
of net.yacy.document.parser.pdfParser$ResourceCleaner
     [java] WARNING: Use --illegal-access=warn to enable warnings of
further illegal reflective access operations
     [java] WARNING: All illegal access operations will be denied in a
future release

Crawling thousands of pdf documents from various sources after
modifications applied, revealed no new memory leak related to pdfbox
(measurements done with JVisualVM).

0 files changed, 0 insertions, 0 deletions