fix(tests): replace libexpect with forkpty() for functional tests

Remove dependency on libexpect which had a segfault bug on Arch Linux.

- Replace exp_spawnl() with forkpty() for PTY creation
- Replace exp_expectl() with custom POSIX regex matching
- Update configure.ac to check for forkpty() instead of libexpect
- Update Makefile.am to link with libutil instead of libexpect/libtcl
- Remove expect/tcl packages from all Dockerfiles
- Add Valgrind suppressions for stabber/pthread false positives

Makefile.am

@@ -290,21 +290,21 @@ tests_unittests_unittests_CPPFLAGS = -Itests/
 tests_unittests_unittests_SOURCES = $(unittest_sources)
 tests_unittests_unittests_LDADD = -lcmocka
 
-# Functional tests require libstabber and libexpect.
-# They are only built when both libraries are available.
+# Functional tests require libstabber.
+# They are only built when libstabber is available.
 # See: https://github.com/profanity-im/profanity/pull/1010
 #      https://github.com/profanity-im/stabber/issues/5
 #
-# Note: Debian/Ubuntu's libexpect requires -ltcl8.6 for linkage.
+# Note: We use forkpty() instead of libexpect for PTY handling.
 
 if HAVE_STABBER
-if HAVE_EXPECT
+if HAVE_FORKPTY
 TESTS += tests/functionaltests/functionaltests
 check_PROGRAMS += tests/functionaltests/functionaltests
 tests_functionaltests_functionaltests_SOURCES = $(functionaltest_sources)
 tests_functionaltests_functionaltests_CPPFLAGS = -Itests/
-tests_functionaltests_functionaltests_CFLAGS = $(AM_CFLAGS) -I/usr/include/tcl8.6 -I/usr/include/tcl8.5
-tests_functionaltests_functionaltests_LDADD = -lcmocka -lstabber -lexpect -ltcl8.6
+tests_functionaltests_functionaltests_CFLAGS = $(AM_CFLAGS)
+tests_functionaltests_functionaltests_LDADD = -lcmocka -lstabber @FORKPTY_LIB@
 endif
 endif