Fix all size warnings calls to ggplot2 (deprecated at 3.4.0).

[BjarkeHautop]

This PR fixes all the size warnings that ggplot2 threw (see also issue #408) by replacing them with linewidth.

I also added size as deprecated in ppc_km_overlay() and p_overlay() using lifecycle::deprecated.

[jgabry]

Thank you! I definitely think we should change all internal cases of this. For the user-facing arguments, is there a reason only to do this for plots in ppc-censoring.R? For example, mcmc_trace() also has a user-facing size argument for controlling line width and I would guess that other functions do too (I haven't done a thorough check recently).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.62%. Comparing base (5a5b1e5) to head (e2b62b9).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #414   +/-   ##
=======================================
  Coverage   98.61%   98.62%           
=======================================
  Files          35       35           
  Lines        5792     5798    +6     
=======================================
+ Hits         5712     5718    +6     
  Misses         80       80           

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[BjarkeHautop]

For the user-facing arguments, is there a reason only to do this for plots in ppc-censoring.R? For example, mcmc_trace() also has a user-facing size argument for controlling line width and I would guess that other functions do too (I haven't done a thorough check recently).

No, we should probably do that. But note that some size arguments are still correct, so we can't just replace all size with linewidth without looking at the code.

[jgabry]

Do mind removing the the deprecations in the ppc-censoring functions from this PR? Let's handle internal changes in this PR and then we can do the user-facing changes separately. I think that will make it easier to review and reason about. Is that ok with you? Thanks again for working on this!

[BjarkeHautop]

No problem! Removed all deprecation stuff.