pgsql: Perl scripts: eliminate "Useless interpolation" warnings

Perl scripts:  eliminate "Useless interpolation" warnings

Eliminate warnings of Perl Critic from src/tools.

Backpatch-through: master

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/43ce181059d4ecbb1b14b75e7f38a7dda9f80225

Modified Files
--------------
src/tools/copyright.pl       |  2 +-
src/tools/gen_export.pl      | 10 +++++-----
src/tools/gen_keywordlist.pl |  4 ++--
src/tools/msvc_gendef.pl     | 10 +++++-----
src/tools/version_stamp.pl   | 18 +++++++++---------
src/tools/win32tzlist.pl     |  2 +-
6 files changed, 23 insertions(+), 23 deletions(-)