Do not prepend v to version

[DimitriPapadopoulos]

Description

Debian expects upstream version to start with a digit. See deb-version(7) man page:

The upstream-version may contain only alphanumerics (“A-Za-z0-9”)
and the characters . + - : ~ (full stop, plus, hyphen, colon,
tilde) and should start with a digit. If there is no debian-
revision then hyphens are not allowed; if there is no epoch then
colons are not allowed.

Tools such as dpkg have started enforcing this rule and bail out with an error message if the version of a DEB package starts with v2.4.3 instead of 2.4.3:

$ sudo dpkg -i ANTs-v2.4.3.post10-g871cad0-Linux.deb
dpkg: error processing archive ANTs-v2.4.3.post10-g871cad0-Linux.deb (--install):
 parsing file '/var/lib/dpkg/tmp.ci/control' near line 374 package 'ants':
 'Version' field value 'v2.4.3.post10-g871cad0': version number does not start with digit
Errors were encountered while processing:
 ANTs-v2.4.3.post10-g871cad0-Linux.deb

Fixes #1503.

[cookpa]

I'm OK with this in principle but would need some time to test it didn't interfere with the runners / releases

[cookpa]

I think this might just work, after reviewing other files. The tags would continue to be vX.Y.Z, but the version built into the project can just be X.Y.Z. Merging for now (after CI testing) then testing the release