xfreerdp: removed unused function
xfreerdp: handle negative mouse coordinates

If the pointer is moved out a window relatives coordinates can get negative
in X.

fixed #1654
build: removed macosx-version-min

fixed #1681
Merge pull request #1682 from bmiklautz/issue_1681

build: removed macosx-version-min
Merge pull request #1667 from bmiklautz/stable-1.0_issue_1654

Stable 1.0 issue 1654