supersize: Remove path attribution for symbol gaps

tools/binary_size/libsupersize/testdata/Console.golden

 # Show pydoc for main types:
 import models
 help(models)
 
 # Show all attributes of all symbols & per-section totals:
 Print(size_info, verbose=True)
 
 # Show two levels of .text, grouped by first two subdirectories
 text_syms = size_info.symbols.WhereInSection("t")
 by_path = text_syms.GroupBySourcePath(depth=2)
@@ skipping 44 matching lines @@
 42137655 d@0x2ddc608  1065132 {no path}
              ** symbol gap 3 (end of section)
 42927559 d@0x2c17740  789904  third_party/container.c
              chrome::mojom::FieldTrialRecorderProxy [vtable]
 43603544 r@0x284e518  675985  {no path}
              ** merge strings
 43705144 d@0x2dffd88  101600  {no path}
              ** symbol gap 3 (end of section)
 43774268 t@0x28f1e0   69124   third_party/icu/ucnv_ext.c
              foo_bar
-43779986 t@0x28f000   5718    third_party/icu/ucnv_ext.c
+43779986 t@0x28f000   5718    {no path}
              ** symbol gap 0
-43784026 t@0x2a1000   4040    third_party/container.c
+43784026 t@0x2a1000   4040    {no path}
              ** symbol gap 1
 43784474 t@0x28f000   448     third_party/icu/ucnv_ext.c
              ucnv_extMatchFromU
 43784626 d@0x2de7008  152     third_party/container.c
              base::android::kBaseRegisteredMethods
 43784720 t@0x2a1000   94      third_party/container.c
              blink::PaintChunker::releasePaintChunks [clone .part.1]
 43784776 d@0x2c176f0  56      third_party/icu/ucnv_ext.c
              ChromeMainDelegate [vtable]
 43784832 d@0x2cd8500  56      third_party/paint.cc
@@ skipping 42 matching lines @@
 43785361 d@0x2de70a4  4       third_party/container.c
              base::android::g_library_version_number
 43785365 d@0x2de70a0  4       third_party/container.c
              base::android::g_renderer_histogram_code
 43785369 r@0x28f3480  4       third_party/paint.cc
              blink::CSSValueKeywordsHash::findValueImpl::value_word_list
 43785373 d@0x2de7000  4       base/page_allocator.cc
              google::protobuf::internal::pLinuxKernelCmpxchg
 43785377 d@0x2de7004  4       third_party/container.c
              google::protobuf::internal::pLinuxKernelMemoryBarrier
-43785380 r@0x284e364  3       base/page_allocator.cc
+43785380 r@0x284e364  3       {no path}
              ** symbol gap 2
 43785380 b@0x0        262144  third_party/fft_float.cc
              ff_cos_131072
 43785380 b@0x0        131072  third_party/fft_fixed.cc
              ff_cos_131072_fixed
 43785380 b@0x0        131072  third_party/fft_float.cc
              ff_cos_65536
 43785380 b@0x2dffe80  200     third_party/icu/ucnv_ext.c
              SaveHistogram::atomic_histogram_pointer
 43785380 b@0x2dffda0  28      third_party/icu/ucnv_ext.c
              g_chrome_content_browser_client
 43785380 b@0x2dffe84  4       third_party/icu/ucnv_ext.c
              g_AnimationFrameTimeHistogram_clazz