remove lcsymtacs (github issue #666)

The lcsymtacs structure is regarded superseded as it plainly is
a shorthand for opening the following modules:
Abbrev HolKernel boolLib Tactic Tactical BasicProvers simpLib
Rewrite bossLib Thm_cont

fix HOL4combinScript.sml with an explicit type annotation

attempt to present combinTheory on top of the OpenTheory stdlib

one assumption remains unsatisfied (despite being proved) for reasons I
do not yet understand