Old syntax in LABEL_DATE

[alaingdl]

(this code is in src/pro/)
Not to forget, I am not sure to have time ti fix it now, but we have old () inside this code instead of [] for array index

../../build_cmake/bin/gdl --trace-old-syntax
GDL> label_date()
old syntax at line 83, column 39
old syntax at line 131, column 45
old syntax at line 208, column 22
% Compiled module: GDL_IMPLIED_PRINT.
           0