Fix documentation of Mat_VarGetNumberOfFields
Fix documentation of Mat_VarGetNumberOfFields

* src/mat.c (Mat_VarGetNumberOfFields): Remove documentation that the
      MAT file version must be 5

tbeu/matio,tbeu/matio,NJannasch/matio,CBL-ORION/matio,martinichka/matio-coder,MaartenBent/matio,tbeu/matio,martinichka/matio-coder,martinichka/matio-coder,CBL-ORION/matio,MaartenBent/matio,MaartenBent/matio,telehan/libmatio,CBL-ORION/matio-sf-mirror,CBL-ORION/matio-sf-mirror,MaartenBent/matio,tbeu/matio,telehan/libmatio,NJannasch/matio