main/linux-*: remove redundant override of HOSTCC
Replacement for !3781 (closed).
apkbuild-lint complains about the use of HOSTCC in APKBUILDs:
IC:[AL6]:main/linux-lts/APKBUILD:66:prefix custom variable with _: HOSTCC="${CC:-gcc}"
IC:[AL6]:main/linux-lts/APKBUILD:67:prefix custom variable with _: HOSTCC="${HOSTCC#${CROSS_COMPILE}}"
MC:[AL31]:main/linux-lts/APKBUILD:66:variables must not have capital letters
MC:[AL31]:main/linux-lts/APKBUILD:67:variables must not have capital letters
The first two were fixed in Leo/atools!24 (merged). But apkbuild-lint still complains about the capitalized variable. Adding an exception for this in atools seems quite complicated.
It turns out overriding HOSTCC in the linux-* APKBUILD is actually no longer necessary. abuild automatically sets HOSTCC correctly now when cross compiling, and the APKBUILD will just set the same value again. (see abuild@9be173c6)
We can just remove HOSTCC from the APKBUILD. linux-lts still builds fine when cross compiling for aarch64 using bootstrap.sh.
Cc: @PureTryOut @fabled