gdb: Fix description for apk, remove backtick

gdb: Fix description for apk, remove backtick

Remove backtick from gdb description text, as that seems to
be recognized as a shell action by compilation with apk,
causing error.

Example from test buildbot:
 rstrip.sh: /builder/shared-workdir/build/sdk/build_dir/target-aarch64_generic_musl/gdb-15.2/ipkg-aarch64_generic/gdb/usr/bin/gdb: executable
 bash: -c: line 1: unexpected EOF while looking for matching ``'
 bash: -c: line 2: syntax error: unexpected end of file
 make[3]: *** [Makefile:123: /builder/shared-workdir/build/sdk/bin/packages/aarch64_generic/base/gdb-15.2-r1.apk] Error 2

Local compilation:
 rstrip.sh: /OpenWrt/aarch64/build_dir/target-aarch64_cortex-a53_musl/gdb-15.2/ipkg-aarch64_cortex-a53/gdb/usr/bin/gdb: executable
 bash: -c: line 1: unexpected EOF while looking for matching ``'
 make[2]: *** [Makefile:123: /OpenWrt/aarch64/bin/packages/aarch64_cortex-a53/base/gdb-15.2-r1.apk] Error 2

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
Link: https://github.com/openwrt/openwrt/pull/16908
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>