analyzer: Remove check of unsigned_char in maybe_undo_optimize_bit_field_compare.

The check for the type seems unnecessary and gets in the way sometimes.
Also with a patch I am working on for match.pd, it causes a failure to happen.
Before my patch the IR was:
  _1 = BIT_FIELD_REF <s, 8, 16>;
  _2 = _1 & 1;
  _3 = _2 != 0;
  _4 = (int) _3;
  __analyzer_eval (_4);

Where _2 was an unsigned char type.
And After my patch we have:
  _1 = BIT_FIELD_REF <s, 8, 16>;
  _2 = (int) _1;
  _3 = _2 & 1;
  __analyzer_eval (_3);

But in this case, the BIT_AND_EXPR is in an int type.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/analyzer/ChangeLog:

	* region-model-manager.cc (maybe_undo_optimize_bit_field_compare): Remove
	the check for type being unsigned_char_type_node.