gnutls: trim down gnutls-devel depends.

[ericonr]

Instead of pulling in all makedepends from gnutls into gnutls-devel,
just use those listed in gnutls's pkgconfig files. This can speed up
local builds and avoids potential dependencies conflicts between
unnecessary packages.

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR