Revert "rhbz#1075124: writerfilter: fix tables with negative left margin"

It appears that this was just a workaround that incidentally worked.
Making the negative value even larger (in abs value) doesn't seem to make
a difference for MSO, but LO fails again. A proper fix (better workaround?)
will follow.

This reverts commit 76aa23c59b4c81ea7b9d974a1a0a9e39c6bf8741.
apparently some table .docx properties shouldn't be < 0

Somewhat related to 10b4da63e3143108ba75891e9e98fdaa2f7953ab , a similar
doc has negative value inside w:tblCellMar, which MSO seems to ignore
(altering the value has no visible effect), so ignore it as well.

Change-Id: I846e9b55fea0d4e66f03ce615584516360b8b7dd
test for ignoring negative cell margin values

Change-Id: I7e56762a7097dd7369f9d8d71b499888ee5c081d