remove unneeded proj config

[ctoney]

This pull request mainly modifies the configure script. It is intended to fix a bug from a test that compiled gdal + proj + sqlite3 after removing all gdal flags and only using proj flags from pkg-config (thanks to debugging by @s-u). The stand-alone PROJ config that was based on pkg-config has been removed. This should not be needed since gdalraster only uses PROJ via GDAL headers. The availability of PROJ via GDAL is still tested and the optional local copy of the PROJ data directory is handled. PROJ version number requirements are dropped since we are only concerned with PROJ availability to GDAL and are not using the PROJ API directly. Some minor clean up in the GDAL config was also done, removing a legacy test related to GDAL > 2.5 or not.

autoconf macros are now used for compiler invocations so they appear in the log (also thanks to feedback from Simon Urbanek).

configure now attempts to get the PROJ data directory from pkg-config if possible. If not, the environment variables PROJ_LIB (deprecated at PROJ 9.1) and PROJ_DATA (PROJ >= 9.1) are checked. The configure argument --with-proj-data is checked last.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (aa0d47e) 83.53% compared to head (4f4f304) 83.53%.

❗ Current head 4f4f304 differs from pull request most recent head 6e75a17. Consider uploading reports for the commit 6e75a17 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #190   +/-   ##
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  Coverage   83.53%   83.53%           
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  Files          17       17           
  Lines        3043     3043           
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  Hits         2542     2542           
  Misses        501      501           

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