bc: stop checking for name length in bc_lex_name()

bc: stop checking for name length in bc_lex_name()

Gigabyte-long names are not a practical concern.

function                                             old     new   delta
bc_lex_name                                           73      69      -4
bc_lex_token                                        1266    1259      -7
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-11)             Total: -11 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>