Remove limitation on font-size writing in PdfCanvas

This check originated from iText 5, where it was statedthat some viewers
might crash because of the too small font-size. However it's convenient
to write /DA key for acro fields via PdfCanvas and in this content
zero font-size is absolutely valid value. In general it seems that
it's should be user responsibility to care of such things.

DEVSIX-1916
DEVSIX-1861

Author: pavel-alay

kernel/src/main/java/com/itextpdf/kernel/pdf/canvas/PdfCanvas.java

@@ -438,8 +438,6 @@ public PdfCanvas endVariableText() {
      * @return      The edited canvas.
      */
     public PdfCanvas setFontAndSize(PdfFont font, float size) {
-        if (size < 0.0001f && size > -0.0001f)
-            throw new PdfException(PdfException.FontSizeIsTooSmall, size);
         currentGs.setFontSize(size);
         PdfName fontName = resources.addFont(document, font);
         currentGs.setFont(font);