quantum: Move qk_ucis_state to process_unicode.c

In order to not declare the same variable in multiple objects (which
happens when building UCIS-enabled keymap for both the ErgoDox EZ and
the ErgoDox Infinity), move the declaration to the .c file, and keep
only an extern reference in the header.

Many thanks to @fredizzimo for spotting the error in Travis, and
suggesting the fix.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

quantum/process_keycode/process_unicode.c

@@ -74,6 +74,8 @@ bool process_unicode(uint16_t keycode, keyrecord_t *record) {
 }
 
 #ifdef UCIS_ENABLE
+qk_ucis_state_t qk_ucis_state;
+
 void qk_ucis_start(void) {
   qk_ucis_state.count = 0;
   qk_ucis_state.in_progress = true;