Remove all existing native *swt* libraries before copying new

If make_common.mak changes, code in 'Check if SWT-binaries build is
needed' stage, that is supposed to delete native libraries, simply
doesn't delete anything as it relies on getSWTVersions() that reads
(changed) versions.

Instead, try to delete every *swt* library file stored in git before
copying freshly compiled ones during 'Collect and sign binaries' stage.

Fixes #1095

Jenkinsfile

@@ -263,6 +263,7 @@ pipeline {
 											done
 										fi
 									fi
+									rm "${WORKSPACE}/eclipse.platform.swt/binaries/org.eclipse.swt.${PLATFORM}/*swt*.$binariesExtension"
 									cp *.$binariesExtension "${WORKSPACE}/eclipse.platform.swt/binaries/org.eclipse.swt.${PLATFORM}/"
 								'''
 							}