Revert "make compatible with Debian jessie (texlive 2014)"

jessie is oldoldstable and only in LTS by now, do not use it
any more for productive projects.

This reverts commit 401c6cac.
And besides, it removes all traces of actual foreign code.

unicodedomino.sty

@@ -46,49 +46,6 @@
  \expandafter\UTFviii@hexnumber\expandafter{#1}%
 }%
 
-% missing in utf8.def 2014/09/29 v1.1m (Debian jessie)
-\ifx\decode@UTFviii\@undefined%
- \PackageWarning{unicodedomino}{Consider updating utf8.def}%
- % taken from utf8.def 2016/02/28 v1.1s (Debian sid), no claims on this code
- \gdef\decode@UTFviii#1\relax{%
-  \expandafter\UTFviii@cleanup\the\numexpr\dec@de@UTFviii#1\relax)))))\@empty%
- }%
- \gdef\UTFviii@cleanup#1)#2\@empty{#1}%
- \gdef\dec@de@UTFviii#1{%
-  \ifx\relax#1%
-  \else
-   \ifnum`#1>"EF
-    ((((`#1-"F0)%
-   \else
-    \ifnum`#1>"DF
-      (((`#1-"E0)%
-    \else
-     \ifnum`#1>"BF
-      ((`#1-"C0)%
-     \else
-      \ifnum`#1>"7F
-       )*64+(`#1-"80)%
-      \else
-       +`#1 %
-      \fi
-     \fi
-    \fi
-   \fi
-   \expandafter\dec@de@UTFviii
-  \fi%
- }%
- \gdef\UTFviii@hexnumber#1{%
-  \ifnum#1>15 %
-   \expandafter\UTFviii@hexnumber\expandafter{\the\numexpr(#1-8)/16\relax}%
-  \fi%
-  \UTFviii@hexdigit{\numexpr#1\ifnum#1>0-((#1-8)/16)*16\fi\relax}%
- }%
- \gdef\UTFviii@hexdigit#1{\ifcase\numexpr#1\relax%
-  0\or1\or2\or3\or4\or5\or6\or7\or8\or9\or A\or B\or C\or D\or E\or F\fi%
- }%
- % end of utf8.def inline update
-\fi%
-
 % override to beautify the output, not strictly necessary but requested
 \gdef\UTFviii@splitcsname#1:#2\relax{%
  #2 (\expandafter\unicodedomino@codepoint\expandafter{%