remove now-unused VERSION file, update changelog

9 jobs for v2.1rc1 in 13 minutes and 33 seconds (queued for 12 minutes and 40 seconds)
Status Name Job ID Coverage
  Test
passed clang-c++11 #83102
Linux

00:01:56

passed cppcheck #83104
Linux

00:03:04

passed doc #83109
Linux

00:00:10

passed gcc-c++11 #83101
Linux

00:01:53

passed macos-c++11 #83103
Apple

00:01:50

passed VS2015-32-bit #83108
VS2015

00:01:26

passed VS2015-64-bit #83107
VS2015

00:01:35

passed VS2017-32-bit #83106
VS2017

00:01:20

passed VS2017-64-bit #83105
VS2015

00:01:29