[ng] tests: remove stale workarounds for non-GNU make

[ng] tests: remove stale workarounds for non-GNU make

* t/yacc-depend2.sh: Remove now-irrelevant comment about
the fact that this test fails with FreeBSD make.
* t/silent8.sh: Remove useless workaround for NetBSD make.
* t/tap-signal.tap: Likewise.
* t/posixsubst-ldadd.sh: Remove useless workaround for
FreeBSD make.
* t/posixsubst-libraries.sh: Likewise.
* t/posixsubst-ltlibraries.sh: Likewise.
* t/posixsubst-sources.sh: Likewise.
* t/posixsubst-tests.sh: Likewise.
* t/distcheck-outdated-m4.sh: Remove workaround for
extra-verbose make implementations (like Solaris make).
* t/distcheck-missing-m4.sh: Likewise.
* t/tap-color.sh: Likewise.
* t/color.test (test_no_color): Likewise.
* t/color2.test (test_no_color): Likewise.
Remove redundant check that parallel make does nor redirect
output to temporary files or named pipes.
* t/tap-color.sh: Likewise.
* t/tap-doc.sh: Do not post-process make output to strip
extra lines printed bu Sun dmake..
* t/tap-doc2.sh: Remove stray comment.
* t/yacc-mix-c-cxx.sh: Just assume that "make -jN" can
run make in parallel mode.
* t/tap-more.sh: Likewise.
* t/dist-formats.tap: Likewise.
* t/yacc-line.sh: Avoid workaround to cater for the
Solaris XPG4 make inability to chain suffix rules.
* t/lex-line.sh: Likewise.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>