build-sys: Remove --enable-experimental-api

It was added for the collections bits, but we made that stable.
It's now just cruft and we're very unlikely to reuse the infrastructure
again.

Motivated by a unit test failure when running from a tarball:
https://github.com/ostreedev/ostree/issues/2313

tests/libtest.sh

@@ -637,12 +637,6 @@ skip_without_fuse () {
     [ -e /etc/mtab ] || skip "no /etc/mtab"
 }
 
-skip_without_experimental () {
-    if ! ostree --version | grep -q -e '- experimental'; then
-        skip "No experimental API is compiled in"
-    fi
-}
-
 has_gpgme () {
     local ret
     ${CMD_PREFIX} ostree --version > version.txt

tests/test-symbols.sh

@@ -31,16 +31,9 @@ if echo "$OSTREE_FEATURES" | grep --quiet --no-messages "devel"; then
 else
     devel_syms=
 fi
-if echo "$OSTREE_FEATURES" | grep --quiet --no-messages "experimental"; then
-  experimental_sym="${G_TEST_SRCDIR}/src/libostree/libostree-experimental.sym"
-  experimental_sections="${G_TEST_SRCDIR}/apidoc/ostree-experimental-sections.txt"
-else
-  experimental_sym=""
-  experimental_sections=""
-fi
 
 echo "Verifying all expected symbols are actually exported..."
-grep --no-filename ' ostree_[A-Za-z0-9_]*;' ${released_syms} ${devel_syms} ${experimental_sym} | sed -e 's,^ *\([A-Za-z0-9_]*\);,\1,' | sort -u > expected-symbols.txt
+grep --no-filename ' ostree_[A-Za-z0-9_]*;' ${released_syms} ${devel_syms} | sed -e 's,^ *\([A-Za-z0-9_]*\);,\1,' | sort -u > expected-symbols.txt
 eu-readelf -a ${G_TEST_BUILDDIR}/.libs/libostree-1.so | grep 'FUNC.*GLOBAL.*DEFAULT.*@@LIBOSTREE_' | sed -e 's,^.* \(ostree_[A-Za-z0-9_]*\)@@LIBOSTREE_[0-9A-Z_.]*,\1,' |sort -u > found-symbols.txt
 diff -u expected-symbols.txt found-symbols.txt
 
@@ -48,9 +41,6 @@ echo "Checking that the example symbol wasn't copy-pasted..."
 if test -f ${devel_syms}; then
   assert_file_has_content_once ${devel_syms} "someostree_symbol_deleteme"
 fi
-if test -f ${experimental_sym}; then
-  assert_not_file_has_content ${experimental_sym} "someostree_symbol_deleteme"
-fi
 assert_not_file_has_content ${released_syms} "someostree_symbol_deleteme"
 
 echo "ok exports"
@@ -59,7 +49,7 @@ echo "ok exports"
 grep -E -v '(ostree_cmd__private__)|(ostree_fetcher_config_flags_get_type)' found-symbols.txt > expected-documented.txt
 
 echo "Verifying all public symbols are documented:"
-grep --no-filename '^ostree_' ${G_TEST_SRCDIR}/apidoc/ostree-sections.txt $experimental_sections |sort -u > found-documented.txt
+grep --no-filename '^ostree_' ${G_TEST_SRCDIR}/apidoc/ostree-sections.txt |sort -u > found-documented.txt
 diff -u expected-documented.txt found-documented.txt
 
 echo 'ok documented symbols'