use strict;
use warnings;

while ( <DATA> ) {
  m/^\s*{name_a\s/   and   s/\bparam_(?:[^xy]\w*|[xy]\w+)\s*=\s*"[^"]*"\s*//g;

  s/\s+}\s*$/}\n/;  # cosmetics
  print;
}

__DATA__
{name_b param_v="wh"}
{name_a param_x="abc" param_a="fsd" param_y="def"}
{name_z param_sd="zka" param_s="df"}
{name_a param_y="wtf" param_z="kro" param_c="ptz" param_ch="www"}
{name_a param_y="wff" param_xyz="xy" param_x="" }