ICU-20969 Fix file permissions (-x) on ICU4C source files.
diff --git a/icu4c/source/common/umutex.h b/icu4c/source/common/umutex.h
old mode 100755
new mode 100644
diff --git a/icu4c/source/i18n/unicode/selfmt.h b/icu4c/source/i18n/unicode/selfmt.h
old mode 100755
new mode 100644
diff --git a/icu4c/source/test/intltest/simplethread.cpp b/icu4c/source/test/intltest/simplethread.cpp
old mode 100755
new mode 100644
diff --git a/icu4c/source/test/intltest/simplethread.h b/icu4c/source/test/intltest/simplethread.h
old mode 100755
new mode 100644