community/glibd: fix for 3.15 builders

Fixes #13143 (closed) as x86_64 also fails on 3.15 builders

Removal of string_new, string_new_len, string_sized_new allows to build

The Meson build system
Version: 0.59.3
Source dir: /home/buildozer/aports/community/glibd/src/GlibD-2.3.0
Build dir: /home/buildozer/aports/community/glibd/src/GlibD-2.3.0/output
Build type: native build
Project name: GlibD
Project version: 2.2.0
D compiler for the host machine: ldc2 (llvm 1.28.0 "LDC - the LLVM D compiler (1.28.0):")
D linker for the host machine: ldc2 ld.bfd 2.37
Host machine cpu family: x86_64
Host machine cpu: x86_64
Found pkg-config: /usr/bin/pkg-config (1.8.0)
Run-time dependency glib-2.0 found: YES 2.70.0
Run-time dependency gmodule-2.0 found: YES 2.70.0
Run-time dependency gobject-2.0 found: YES 2.70.0
Run-time dependency gio-2.0 found: YES 2.70.0
Run-time dependency gobject-introspection-1.0 found: YES 1.70.0
Program girtod found: YES (/usr/bin/girtod)
Message: Generating D interfaces from GIR...

meson.build:35:4: ERROR: Problem encountered: Unable to build D intefaces from GIR:
Error /home/buildozer/aports/community/glibd/src/GlibD-2.3.0/src/APILookupGLib.txt(1988): Unknown function string_new


A full log can be found at /home/buildozer/aports/community/glibd/src/GlibD-2.3.0/output/meson-logs/meson-log.txt
>>> ERROR: glibd: build failed