build: Simplify pkg-config file generation

Meson 0.45 can automatically build the Requires line from a list of
dependencies, rather than us having to maintain two separate lists.

This bumps our Meson dependency to 0.45.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
2 jobs for pc-requires in 2 minutes and 58 seconds (queued for 17 minutes and 2 seconds)
Status Job ID Name Coverage
  Build
passed #115253
build-job

00:01:28

 
  Test
passed #115254
test

00:01:30

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