configure: Remove header check for ICU
configure: Remove header check for ICU

It wrongly detects old versions of ICU as valid.
Checking with pkg-config is sufficient and also sets ICU_UC_LIBS.

Signed-off-by: Stefan Weil <8d4c780fcfdc41841e5070f4c43da8958ba6aec0@weilnetz.de>

UB-Mannheim/tesseract,jbarlow83/tesseract,stweil/tesseract,jbarlow83/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,jbarlow83/tesseract,UB-Mannheim/tesseract,stweil/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,UB-Mannheim/tesseract,jbarlow83/tesseract,UB-Mannheim/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,stweil/tesseract,stweil/tesseract,stweil/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,jbarlow83/tesseract