Delete param_attr in docs

doc/fluid/api/gen_doc.sh

 #!/bin/bash
 python gen_doc.py layers --submodules control_flow device io nn ops tensor learning_rate_scheduler detection metric_op > layers.rst
 
-for module in data_feeder clip metrics executor initializer io nets optimizer param_attr profiler regularizer transpiler recordio_writer backward average profiler
+for module in data_feeder clip metrics executor initializer io nets optimizer profiler regularizer transpiler recordio_writer backward average profiler
 do
   python gen_doc.py ${module} > ${module}.rst
 done