tools: remove redundant Python event data structure definitions (#2204)

Simplify code following #2198 (https://github.com/iovisor/bcc/pull/2198).

Some tools are not touched: mountsnoop.py, trace.py, lib/*.py, old/*.py.
diff --git a/tools/bashreadline.py b/tools/bashreadline.py
index da9c1b7..af4f18e 100755
--- a/tools/bashreadline.py
+++ b/tools/bashreadline.py
@@ -14,7 +14,6 @@
 from __future__ import print_function
 from bcc import BPF
 from time import strftime
-import ctypes as ct
 
 # load BPF program
 bpf_text = """
@@ -40,13 +39,6 @@
     return 0;
 };
 """
-STR_DATA = 80
-
-class Data(ct.Structure):
-    _fields_ = [
-        ("pid", ct.c_ulonglong),
-        ("str", ct.c_char * STR_DATA)
-    ]
 
 b = BPF(text=bpf_text)
 b.attach_uretprobe(name="/bin/bash", sym="readline", fn_name="printret")
@@ -55,7 +47,7 @@
 print("%-9s %-6s %s" % ("TIME", "PID", "COMMAND"))
 
 def print_event(cpu, data, size):
-    event = ct.cast(data, ct.POINTER(Data)).contents
+    event = b["events"].event(data)
     print("%-9s %-6d %s" % (strftime("%H:%M:%S"), event.pid,
                             event.str.decode('utf-8', 'replace')))