scripts/mksysmap: remove comments described in nm(1)

#####

# Generate System.map (actual filename passed as second argument)

# $NM produces the following output:

# f0081e80 T alloc_vfsmnt

#   The second row specify the type of the symbol:

#   A = Absolute

#   B = Uninitialised data (.bss)

#   C = Common symbol

#   D = Initialised data

#   G = Initialised data for small objects

#   I = Indirect reference to another symbol

#   N = Debugging symbol

#   R = Read only

#   S = Uninitialised data for small objects

#   T = Text code symbol

#   U = Undefined symbol

#   V = Weak symbol

#   W = Weak symbol

#   Corresponding small letters are local symbols

# The following refers to the symbol type as per nm(1).

# For System.map filter away:

#   a - local absolute symbols