remove unused variables from .pc files

See merge request lscsoft/lalsuite!1802

Fix data package type

See merge request lscsoft/lalsuite!1799

Fix up RPM handling for noarch

See merge request lscsoft/lalsuite!1803

- for some reason that I don't understand the .pc files contain a number of variable definitions that are not required by pkg-config.  the configure script sets two of these of these unused variables to values that, in turn, depend on other variable definitions that are not included in the .pc file and are not expanded at configure time.  this causes pkg-config to report an undefined variable error, and makes software that links to lal impossible to compile if pkg-config is relied upon to supply compiler and linker falgs.
- the cause of the problem is an incompatibility between some versions of the AM_PATH_PYTHON script and some versions of autoconf/automake/autosomething.  the bug has been reported in numerous forums for example https://debbugs.gnu.org/cgi/bugreport.cgi?bug=35322 and I believe it has been fixed upstream, however it is not fixed in lalsuite and/or the versions of the build tools installed on some user's computers, and it likely won't be for some time...

non-x86_64 in general

[skip debian][skip conda][skip coverage][skip docs][skip wheels][skip docker][skip compiler][skip platform]

Revert "Merge branch 'gitlab-default-mr-template' into 'master'"

See merge request lscsoft/lalsuite!1798

This reverts merge request !1797

Set default merge request template under .gitlab/merge_request_templates/

See merge request lscsoft/lalsuite!1797

Discussed on lscsoft/lalsuite#447

[skip compiler] [skip conda] [skip coverage] [skip debian] [skip docker] [skip docs] [skip docs] [skip integration] [skip lint] [skip platform] [skip rhel] [skip wheels]

[skip compiler] [skip conda] [skip coverage] [skip debian] [skip docker] [skip docs] [skip docs] [skip integration] [skip lint] [skip platform] [skip rhel] [skip wheels]

Merge release branch

See merge request lscsoft/lalsuite!1796