gnupg2: don't preserve the old gpg2 executable name

gnupg2: don't preserve the old gpg2 executable name

Commit e82fadab236a (gnupg2: bump to version 2.2.0) added a configure
option to keep the old 'gpg2' executable name to avoid conflict with the
gnupg package. It turns out that gnupg depends on !BR2_PACKAGE_GNUPG2
since commit 2cadb26e6d4 (gnupg: make gnupg and gnupg2 mutually
exclusive). Drop this configure option.

Rename the config option that controls the removal of gpgv2, now gpgv,
to match the new name. Add legacy config symbol handling.

Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>