software/theia: Adjust to Caddy build changes
The changes to the caddy build method in https://lab.nexedi.com/nexedi/slapos/commit/1cfb657f05e3fd2d9e8b220c0945f8001104205f break software/theia because software/theia installs the go language server gopls (see https://lab.nexedi.com/nexedi/slapos/commit/5a7fffa540fe9ef9c30b2f373fe8ab78e49ce959) and at some point this required extending the previous caddy build method to make go installs both caddy and gopls (see https://lab.nexedi.com/nexedi/slapos/commit/f56c476a5fe5a9c1baa3547e76a623d5883be95d).
See this test result showing the problem
Fix software/theia by removing the now obsolete extension of the caddy build method and dropping gopls (which wasn't quite working anyway) in the same move.
EDIT: instead of dropping gopls, upgrade to gopls@v0.6.6 which can be installed using the standard go install method.