golang: Drop support for Go1.14

This Go release is EOL now.

Don't drop support for Go1.12 and Go1.13 yet. Even though those Go releases are
also EOL since long ago, they are still being used inside SlapOS:

Go1.12 - by gitlab  (/cc @jerome, @alain.takoudjou)
Go1.13 - by galène  (/cc @tomo, @alain.takoudjou)

component/golang/buildout.cfg

@@ -51,15 +51,6 @@ md5sum = 4f4af14d88352a62761a9dcedf863ac0
 environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
-[golang1.14]
-<= golang-common
-url = https://golang.org/dl/go1.14.15.src.tar.gz
-md5sum = 1065b705a0d330136084f4e1628baf82
-
-# go1.14 needs go1.4 to bootstrap
-environment-extra =
-  GOROOT_BOOTSTRAP=${golang14:location}
-
 [golang1.15]
 <= golang-common
 url = https://golang.org/dl/go1.15.10.src.tar.gz