glib: Drop G_GNUC_MALLOC usage from various other allocation functions

These functions may be OK to leave the G_GNUC_MALLOC attribute on,
because the only valid pointers in the storage areas they return are,
themselves, new pointers.

However, it’s a lot easier to remove the attributes now than to try and
diagnose miscompilations in future. The performance impact of this is
likely to be unmeasurable. If there are performance problems caused by
this, then they can be profiled and fixed case-by-case in future,
bearing in mind the possibility for miscompilation if G_GNUC_MALLOC is
readded.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

GNOME/glib#1465
8 jobs for 1465-bye-bye-g-gnuc-malloc in 11 minutes and 49 seconds (queued for 11 seconds)
Status Job ID Name Coverage
  Build
passed #88527
cross-android_api21_arm64

00:01:41

passed #88528
cross-android_api28_arm64

00:01:36

passed #88529
cross-mingw64

00:02:08

passed #88526
fedora-x86_64

00:04:25

manual #88532
freebsd-11 allowed to fail manual
freebsd-11-x86_64
passed #88530
win32
msys2-mingw32

00:08:01

passed #88531
win32
vs2017-x64

00:05:33

 
  Coverage
passed #88533
coverage

00:01:44

73.3%