Remove erroneous quotes from sed command line.

[oursland]

As noted by https://github.com/FreeCAD/FreeCAD/pull/15366#discussion_r1675799471, an extra set of quotation marks were included in the osx variant of this script.

[adrianinsaval]

could you rebase so CI runs? IIRC this was done on purpose, sed is weird on macos and fails without that empty string. You'll notice it's not the only instance where do that in the script

[adrianinsaval]

stackexchange says it's because macos ships BSD's sed where a suffix argument is mandatory while linux ships with GNU sed where it's optional: https://stackoverflow.com/questions/16745988/sed-command-with-i-option-in-place-editing-works-fine-on-ubuntu-but-not-mac so the empty string is not wrong there