[mono] remove unneeded PKG_CONFIG_PATH for FreeBSD (#84062)

Author: Thefrank

src/mono/mono.proj

@@ -360,7 +360,6 @@
     <ItemGroup Condition="'$(TargetsFreeBSD)' == 'true' and '$(MonoCrossDir)' != '' and '$(TargetArchitecture)' == 'arm64'">
       <_MonoCMakeArgs Include="-DCMAKE_TOOLCHAIN_FILE=$(CrossToolchainFile)" />
       <_MonoBuildEnv Include="TARGET_BUILD_ARCH=arm64" />
-      <_MonoBuildEnv Include="PKG_CONFIG_PATH=$(MonoCrossDir)usr/local/libdata/pkgconfig" />
     </ItemGroup>
 
     <!-- Windows specific options -->