software/theia: Adjust to Caddy build changes
The changes to the caddy build method in 1cfb657f break software/theia because software/theia installs the go language server gopls (see 5a7fffa5) and at some point this required extending the previous caddy build method to make go installs both caddy and gopls (see f56c476a).
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.