lib: Remove invalid G_GNUC_WARN_IF_UNUSED annotations
lib: Remove invalid G_GNUC_WARN_IF_UNUSED annotations

pwithnall/uhttpmock,MathieuDuponchelle/uhttpmock,pwithnall/uhttpmock,MathieuDuponchelle/uhttpmock,Distrotech/uhttpmock,MathieuDuponchelle/uhttpmock,Distrotech/uhttpmock